Was Genesis generally considered to be literal by theologians in the Middle Ages and Renaissance? I know Maimonides didn't. Were there any others?
I don't know much about this, but as far as I can tell, it's the kind of thing that people didn't really comment on much. In those times there weren't any rival theories of the origins of the universe and of human beings, so there was no particular reason for anyone to suppose that Genesis wasn't literally true - it was the only horse in the race. The exception to that is if they had theological or philosophical reasons to think otherwise, as Origen had. So I don't believe you'll generally find discussions by medieval theologians about whether Genesis is literally true, one way or the other - it wasn't an issue for them.
Another thing I forgot to ask; I've heard that Christianity in Europe was tied to nationalism. Each country tried to become the "savior state" and that gave birth to legends such as Joan of Arc. During the French revolution, there was a backlash against Christianity as the King was executed and the new rulers promised a liberal constitution. The fall of nationalism therefore could have prompted the exodus from religion we see in Europe today. What would you say about this theory?
I don't find that convincing. For one thing, there was precious little "liberal" about the Jacobins. More importantly, there was no backlash against Christianity. The Jacobins attempted to replace Christianity with a sort of deism, but this was a wholly top-down effort. The ordinary people weren't remotely interested in deism, and after the fall of the Jacobins Catholicism promptly returned to its central place in French society. It wouldn't lose it for many decades, perhaps even a century, and for quite different reasons.
Also, I don't know what you mean by "the fall of nationalism". Isn't nationalism as alive and well as it ever has been? In this country we are, after all, preparing for the possibility of Scotland going its own way.
The exodus from religion that you mention is certainly a real phenomenon, but it is extremely poorly understood. No-one can agree on how substantial it is, when it began, or what caused it. Some would say that much of western Europe is now almost entirely unreligious, while others would say that actually religion remains very strong even in e.g. Britain or Scandinavia. This is partly because no-one can agree on how to measure religiosity. Some would say that the decline began in the early twentieth century or even before, while others would date it only to after the 1960s. And as for the causes, that's anyone's guess.
Let's say that there was never any Christianity or Islam to convert idolaters or spread the worship of God. Would pagan beliefs have survived into the modern era? For instance, would it be acceptable to worship trees and bushes as gods even if everyone knew that they were simply mindless clumps of organic matter that had gained the ability to self-sustain through natural selection? In India they still worship cows, although I think that is because of the reincarnation belief (which still survives despite knowledge of biology) and not because cows are gods or anything like that.
What about the weather? Surely no educated person today would worship Thor? We know that lightning is simply a massive discharge or energy caused by the unbalanced flow of electrons inside a cloud, and unlike in monotheism, nature was not simply considered a tool of the higher power(s), but rather was the direct supernatural act of the gods. The same goes for the sun... we couldn't worship Ra as the creator of the universe if we knew what the sun actually was and its relationship with the rest of the stars (the entirely galaxy couldn't have come from the sun). Interestingly, if not for the rise of monotheism the world right now might be overwhelmingly atheist as people discovered the nature of their deities and gradually abandoned them. Buddhism and others similar to it might spread to fill the gaps, though.
This is an interesting question. But I think that Eran is right to question your assumptions about why people believe what they do.
First, you have to distinguish between the historical origins of a belief and the reasons why people hold it today. It's perfectly possible, for example, that belief in a god or gods first arose as an attempt to explain natural phenomena. But it doesn't follow that people in later centuries who believe in the same gods do so for that reason. An illustration: Charles I tried to force his way into parliament in 1642 to arrest several MPs. Ever since, the monarch's representative, Black Rod, has had the door to the Commons slammed in his face as part of the state opening of parliament. Why? Not because anyone is really trying to stop the Queen from coming in, but simply because it's always been done that way, at least for the past three and a half centuries. Religion is like that too.
Second, it's often assumed today that early religious beliefs arose as a sort of primitive attempt at science, to explain otherwise inexplicable natural phenomena, but in fact there's no evidence for this. Indeed if you actually look at early religious texts you'll find that while natural events are blamed on the gods, people spend relatively little time thinking about this sort of thing, and instead are interested in the gods mainly in the ways they relate to human beings. Consider, for example, the fact that most ancient cultures had a goddess of love and a god of war. Presumably ancient people didn't think that love and war required any particular explanation for their existence, supernatural or otherwise. Rather, the gods in question were anthropomorphisations of elements of human nature that they thought significant. The tendency of ancient people to associate gods with particular places - rivers, hills, crossroads, etc. - also suggests that, to them, gods were detectable presences in the world, believed in primarily because people had a sense of the holy and numinous. The fact that gods could be appealed to as explanations of otherwise mysterious phenomena would then be just a nice bonus rather than the original motivation for the belief.
Either way, belief in gods is quite capable of surviving the discovery that you can explain everything in nature naturally, as you can see by the fact that plenty of people manage to believe in God while not thinking him responsible for thunderbolts and the like. They even manage to believe in multiple gods, as the existence of well educated Hindus also indicates. Hinduism is surely the most obvious example of a pre-Christian paganism that not only survives but thrives today.
The issue of worshipping natural objects is rather different. First, of course, many people do worship trees and the like today, even apparently sensible people who understand science. The reason, as Jehoshua says, is that they distinguish between the physical object and the spirit being worshipped (rather as monotheist Christians can distinguish between the object being venerated, e.g. a relic or an icon, and the object of worship, i.e. God). In fact ancient pagans made the same distinction. The pagan philosopher Celsus, criticising Christians for ridiculing pagans for worshipping idols,
said:
Celsus said:
If they merely mean that the stone, wood, brass, or gold which has been wrought by this or that workman cannot be a god, they are ridiculous with their wisdom. For who, unless he be utterly childish in his simplicity, can take these for gods, and not for offerings consecrated to the service of the gods, or images representing them?
As a second-century middle Platonist philosopher I'm sure that Celsus wasn't typical of ancient pagan beliefs, and no doubt many ordinary people did assume that the images actually were gods. But it shows that the conceptual space existed, as it still does, by which an intelligent person can defend these practices.
If monotheism had never emerged, I'm sure that polytheistic religion would still be widespread, just as it is in India. I certainly don't see any reason to think that religion ever could have dwindled away or is at all likely ever to do so. Religion develops and takes many forms, and is not universal to humans, but it is a common expression of tendencies and attitudes which are universal. It won't go away unless human beings themselves change.
I've tried to consult the wikipedia page on this, and it's been no help at all. In fact, I emerged more confused than before. So I turn to you:
What is the Logos? Why does this word, which translates as "word," mean that God, Jesus, and the Holy Spirit must be the same thing, and yet different things?
It doesn't mean that. The idea that the Father (not "God", as they're all God), the Son, and the Holy Spirit are the same thing yet different things is the doctrine of the Trinity. That doctrine isn't conveyed by the word "Logos". This word really reflects an earlier time, before the development of the doctrine of the Trinity, and conveys rather different ideas.
Basically, Greek is a rather horrible language where any given word can mean all sorts of things. "Logos" is the worst. It does mean "word", but it also means "reason", "thought", "principle", "discourse", "speech", and a host of other things besides. Thus Justin Martyr can say that anyone who lives according to reason (
logos) is actually following Christ, because Christ is the divine Logos. Tertullian can say that the divine Logos existed within the Father before the ages, because it was literally his capacity for reason (
logos) before the Father spoke it and it became his Word (
logos). In other words, the slipperiness of the language could be put to interesting theological use.
Matters are complicated by the fact that
logos was also a technical philosophical term. It was used by the Stoics to refer to the fiery, rational principle that they believed was immanent in the universe and was the ultimate explanation for it, and which might or might not have been identical with God (the Stoics were not entirely self-consistent). Worse, middle Platonists were quite capable of taking this term and using it to refer to their equivalent of the Stoic
logos, the World Soul, an immaterial subsidiary deity, beneath the High God, which had the unenviable job of running the physical universe.
Complications reach their high point when we take into account the fact that these Greek philosophical ideas, and their associated jargon, influenced Jewish ideas about God's Wisdom, which in some passages of the Old Testament and other books takes on qualities very like the Platonic World Soul or the Stoic Logos.
Thus we find Philo of Alexandria, a highly hellenised Jewish philosopher who lived at roughly the same time as Jesus, using the term
logos constantly in his writings. He means it in the middle Platonic sense but finds the doctrine in the Jewish scriptures, which he interpreted allegorically as teaching, well, middle Platonism.
Any or all of these ideas might have lain behind the use of the term
logos in the opening of John's Gospel. Scholars fiercely debate whether John was thinking of, or even aware of, the technical use of the term by philosophers. If he was, then the text's meaning is clear: John is saying that Christ is identical with the Stoic or Platonic Logos, a divine or quasi-divine being that acts as the founding principle of the universe.
It is also uncertain whether John knew the work of Philo and whether he should be interpreted as using the terminology in a similar way to Philo. Or, perhaps, his inspiration is wholly to be found in the Jewish Wisdom tradition, in which case any influence from Greek philosophy is only indirect at best.
There are only a couple of verses about the Logos in John's Gospel, and the idea doesn't recur elsewhere in the New Testament (not even in the rest of the Gospel, unsurprising since the prologue was apparently an adaptation of an already-existing hymn, which the author or editor has incorporated into the Gospel at a relatively late stage of its composition). The people who really developed the idea were the second-century apologists, most notably Justin Martyr, and later Tertullian and Origen. Here again no-one really knows what earlier writers these people were familiar with, but there's no doubt at least that they were highly familiar with philosophical vocabulary and used the logos idea in the light of middle Platonism in particular. In Justin's hands the Christian Logos is simply the World Soul of Platonism, an intermediary between God and the world. Calling Christ "Logos" thus was a way of expressing how he relates to the physical universe.
Later, with Tertullian and Origen, the meaning changed somewhat, and "Logos" became a way of expressing the relation between Christ and the Father. The Logos was less the quasi-divine mediator and more the expression of the Father's mind.
This laid the foundations for the later Trinitarian theology, which was much clearer and better worked out than the Logos theology ever had been. Of course there wasn't a clear leap from the one to the other, and the term "Logos" would continue to be used to refer to the second person of the Trinity, but the particular connotations attached to that term in the second century and perhaps earlier were sidelined.
Also, what is the importance of the Holy Spirit? Why does it deserve to be a "third nature of God?" Why can't it just be God who goes down and impregnates Mary? What's the point in having the third aspect of God to further muddle an already confusing set of circumstances regarding who is and isn't what, and who and was is and isn't divine? If God is omnipotent, then why didn't he know that in a few hundred year a guy named Occam would come up with a cool logical rule that could be applied to this?
The Holy Spirit is the third person, not the third nature, of God. God has only one nature, but that nature exists in three persons (just as human nature exists in many human persons). So it is God who impregnates Mary, because the Holy Spirit is God. The idea of the Holy Spirit is a Jewish one - you find it in Philo as well - so the Christians naturally inherited it. It basically means the activity of God in the world. Now from what I've just said you might think that that sounds a lot like the Logos, and you'd be right. The second-century Logos theologians accordingly had very little concept of the Holy Spirit at all. Justin thought that all interactions between God and the world were done by the Logos, which left no role for any Holy Spirit.
But of course the New Testament mentions the Holy Spirit quite often, so there's no avoiding it, and as time went by Christians came to believe more clearly that the work of sanctifying believers is distinct from that of saving them, but it is equally a divine work. The Holy Spirit is therefore distinct from the Son (as implied by the fact that in the New Testament Jesus sends the Spirit), but still divine. In fact it's quite striking how quickly the issue of the Holy Spirit was settled, in the latter stages of the Arian conflict. Some people accepted the divinity of the Son but not that of the Spirit. The Cappadocian Fathers directed a lot of their attention to these "Pneumatomachi" ("Spirit-fighters") and they seem to have melted away pretty quickly.
, also known as CINO's (Catholics in name only), cafateria catholics, heretics, apostates etc etc.
What I meant by nationalism was extreme nationalism, such as in the Third Reich or the driving force behind colonialism. I think that the shock of losing their empires, which had been justified by religious means, might have contributed to it. Nationalism obviously isn't entirely gone as you pointed out, but it's nothing like it was just 70-80 years ago. Today Europe contains some of the least patriotic countries in the world, while America, the Western nation that has avoided this mass apostasy, is one of the most patriotic. We can observe how this happens, as America's extreme right-wingers have seemed to have turned the Constitution into a holy document. Check this 
