I'm not sure precisely when and how this idea arose, but I suppose it must have had something to do with the practice of praying for the dead. If the dead need our prayers then they can't all be happily arrived in heaven. The passage from the Bible normally cited in support of this practice is II Maccabees 12:39-45. It's worth pointing out that this is, as far as I know, the only doctrinal matter that is affected by whether you accept the Apocrypha as canonical or not, since II Maccabees is deuterocanonical, and there is no passage in any of the universally accepted books that supports this.
You keep saying "practical", but religion isn't just about practicality! It's also about mystical devotion to God. Now from the Orthodox point of view, the Father is worshipped as the ultimate source of divinity, the wellspring of the other two Persons. The doctrine of the double procession of the Holy Spirit undermines that view because it makes the Son the partial souce of the Spirit too. And it is symptomatic of the post-Augustinian approach to the Trinity, which denies that the Father is identical with the divine nature, and instead conceives of a divine nature distinct from any of the three Persons. For many Orthodox theologians, to divorce the divine nature from the Father is to turn it into a meaningless abstraction, and effectively to de-divinise the Father. Now that may have no "practical" consequences, but that's not the point - it has important spiritual consequences, at least in the eyes of those Orthodox who reason along these lines.
I didn't say they were right to deny that "moral choice" is essential to moral responsibility - I said they were right to deny that contra-causal free will is essential to moral responsibility. In fact I don't think that contra-causal free will is really a coherent doctrine at all, let alone either a plausible one or a true one. Even if in fact it is both coherent and true, I don't think that it needed to have been true in order for there to be moral responsibility.
According to those who believe in contra-causal free will, a free act is one that is not (fully) determined by preceding events and states. Which effectively means that you could re-run the universe (as it were) up to the point at which that free act was performed, and it might not be performed. The reason I think this view is incoherent is that that is the normal definition of a random event, but proponents of contra-causal free will also insist that a free act is not a random one. And I don't really see how that is possible. But whether it's possible or not, I don't see what relevance it has to moral responsibility. I think that you're responsible for your actions if you did them (as opposed to being forced to by someone else) and you know what you're doing. You don't have to accept any bizarre metaphysical views about the nature of causation to think that.
I haven't. What's it about?
That is a very common view. I think it's probably the mainstream one. However, it's completely unbiblical; there's no suggestion anywhere in the Bible that there are different "parts" to the Old Testament Law, let alone that one can distinguish neatly between "civil", "ritual", and "moral" sections. Indeed, Paul's letter to the Galatians is concerned, in large part, to argue that you can't pick and choose with regard to the Law; Paul insists that if the Galatians think they ought to be circumcised then in order to be consistent they should be keeping the whole of the Law.
That is exactly the sort of reason why Locke-style latitudinarianism was only a passing historical phenomenon. By which I mean...
Locke's paraphrases of Biblical books are very good. He wasn't really an original theologian, but he is interesting from a theological point of view because of the way he represents the latitudinarianism of his time. Latitudinarianism was a sort of halfway-house to deism. Latitudinarians believed that religion should be reasonable and rational; they believed that reason supported most of the traditional Christian doctrines, but they seem to have been happy to be less certain about those doctrines that they thought weren't so supported by reason. So Locke, for example, insists in his Essay that God's existence can be demonstrated more certainly than anything else (and gives a pretty feeble argument for it), but that's pretty much it. In The reasonableness of Christianity he spends much time arguing that Jesus was the Messiah, and seems to think that this is the main doctrine in Christianity, but he has very little to say about the atonement or the Trinity. The implication is that these doctrines are less easily supported by reason.
What happened next (and indeed was already happening as Locke was writing) was that some people accepted the basic principle that all religious doctrines should be supportable by reason, and concluded that there's no need for revelation at all. Locke had believed that reason and revelation support each other; revelation tells us what's true, but reason tells us that we are dealing with revelation in the first place. The deists simply dropped revelation altogether and sought to construct a wholly rational religion that wouldn't appeal to revelation or to faith at all. And that involved dropping even more traditional Christian doctrines, to the extent that the French deists typically regarded themselves as anti-Christian philosophers (the English and American deists, by contrast, usually regarded themselves as reforming Christians).
Even deism didn't last all that long, because the intellectuals eventually concluded that none of the arguments in favour of religious doctrines really worked. Since they were committed to believing only what was rational, they rejected religion altogether. And that was largely the state of theology by the end of the eighteenth century, but fortunately Schleiermacher and Kierkegaard came along, together with the whole Romantic movement, to suggest that maybe this whole "reason" thing was misguided anyway!
No, because that passage (like most of John) doesn't use the title "son of God", but simply "the Son", which is different. Certainly John doesn't use the title "Son" in anything like the way in which the title "son of God" would normally be used at that time. I suspect that the title was based upon the title "son of God", but John is using it in his own way.
I'm not sure what you mean by "impossible". Do you mean - has anyone tried to show that the supposed proofs of God's existence do not work? Of course! In fact most of the arguments against them were produced by other theists (for example, Aquinas argued against Anselm's ontological proof). And of course I think that most philosophers today would regard the traditional proofs for God's existence as fundamentally flawed (obviously, since most philosophers aren't theists). And quite right too, in my opinion.
I find it an interesting subject, though.
