Could you please explain...
1. Patriarchal blessings? Honestly, they seem to me to be no more efficacious than ones daily horoscope
Patriarchal blessings are revelations given for a specific person. They always contain a statement about one's lineage (i.e., which tribe of Israel a person belongs to), and then contains additional counsel as the Spirit directs the Stake Patriarch who gives the blessing. Blessings are usually given to teenagers when they feel they are ready and pass a worthiness interview; members can choose to delay the blessing and receive it later (or, if they were baptized later in life, can receive it sometime after their baptism). The blessings are usually about 1-2 pages in length (typed, single-spaced). Most people usually only receive one in their lifetime; I have heard of people receiving a second one under unusual circumstances (such as when everything in the first blessing has already been fulfilled).
Many LDS members re-read their blessings regularly, and look to them for guidance and inspiration. We consider them to be sacred and personal, so we don't generally share them with just anyone. My wife and I shared ours during our courtship, after we were engaged to be married. Every year or so we read each others' blessings again (in addition to regularly reading our own).
Promises made in a patriarchal blessing are always dependent upon the faithfulness of the recipient. For example, if your blessing said that you were to be blessed with many children and that you would teach them the Gospel...obviously, you could choose to go a different path, leave the church, choose to never have children, etc. We don't consider the promises to be predestined or fated in any way. Rather, they give direction about what God has in store for you if you stay on the right path.
Questions sometimes come up like "What about Elder Johnson who died while he was a missionary, and his patriarchal blessing said he would be married in the temple and have children?" These promises may be fulfilled in this life or the next, if one is faithful.
2. The role that plural marriage plays in the LDS Church's soteriology?
Soteriology is a word I am unfamiliar with, but wikipedia calls it "the study of religious doctrines of salvation." You may need to be more specific. If you are asking whether we believe plural marriage is necessary for salvation or plays a role in salvation, that is still a difficult question to answer. You may want to read Michael Quinn's research (
http://www.lds-mormon.com/quinn_polygamy.shtml) on post-Manifesto polygamy (from 1890-1904) for some insight into the attitudes and beliefs we had about polygamy at the time of the Manifesto, which differs from attitudes held today.
At the time, some members believed that polygamy was necessary for salvation. Some offshoots in the Mormon movement still teach this idea. It accounts for some of the resistance to giving up polygamy that resulted in the second Manifesto in 1904, which clarified that the practice was to be ended entirely.
I am of the opinion that there will not be polygamy in the next life, and that anyone who has been sealed to more than one spouse will have things worked out in a one-to-one arrangement. All worthy members who have received the necessary ordinances and kept their covenants will have the opportunity to be sealed to a spouse. I realize that this is a minority view, but if you want references, you may want to read Eugene England's essay in Dialogue (volume 20, issue 4, pages 138-154) entitled, "On Fidelity, Polygamy, and Celestial Marriage."
3. As every prophet declared from Brigham Young to Spencer W. Kimball, Blacks were to be excluded from the priesthood because their weren't valiant in the pre-existence, which was made evident because they were born into bodies of the accursed black-skinned bloodline of Cain. Since the 1978 Declaration on the Priesthood, have Black people magically become un-cursed?
You could put it that way.
I believe that the restriction was removed when the Lord spoke to His prophet, the First Presidency, and the Quorum of the Twelve on the matter and revealed to them that the long-awaited time had come. I lived in Salt Lake City at the time, and there was a great deal of rejoicing when the revelation was announced. I have since heard of people leaving the Church over the matter, but almost everyone I have ever met was looking forward to the day when blacks would receive the priesthood. Many believed that it wouldn't happen in their lifetimes, and were very surprised. Very soon after the announcement, Bruce R. McConkie--who is famous for having put "authoritative" speculative statements about why blacks didn't have the priesthood in his book, Mormon Doctrine--was scheduled to give a talk to Institute Directors (who run the church's educational system). He started off with saying, "Brethren, never write a book." The room burst into laughter, because the question on everyone's mind was, What will this apostle say after he's just been shown to be wrong? (he made statements about the issue in his first edition that were later removed, but which he was never allowed to forget by critics). Suffice it to say, people can be wrong, and rather than going off of what one person says, even if he is a General Authority, we should stick to what is doctrinally sound. By the way, just because a statement is in a book titled "Mormon Doctrine" doesn't make it Mormon doctrine, even if it was written by an apostle. To be official doctrine, it must be ratified by the First Presidency, Quorum of the 12, and put to a vote by the general church membership. The 1978 revelation on priesthood followed this order. Bruce R. McConkie's speculative statements about why blacks had not received the priesthood had only been ratified by his publisher.
4. Related to the previous two points, there is a common LDS slogan: "A living prophet trumps a dead one". With this in mind, how would you feel if Thomas S. Monson were to receive a revelation tomorrow that permitted homosexuals to be sealed in the temple, or women to receive the priesthood?
Actually, I haven't heard it put exactly that way. But yes, it is vital that we listen to the living prophet, because God is not dead or mute or indifferent to his creation, and He is constantly revealing his will through his servants. For example, John Taylor once stated that polygamy would never be discontinued in the church, and some offshoot groups have taken that to mean that Wilford Woodruff, his successor, by whom the 1890 Manifesto was issued, was a fallen prophet. It is important for each of us to have a personal testimony or witness that the living prophet is truly a prophet of God and His spokesman to the world at the given time. If we receive such a witness by the Spirit, it becomes much less complicated to accept changes (which will inevitably come).
I do not believe that we will see homosexuals receiving sealings. What we may see is greater clarification about cases involving transsexuals, transgendered individuals, and intersexuals. That is the real gray area, where there is a doctrinal leg to stand on, so to speak, for someone who might not fit the usual pattern of gender assignments (for example, an intersexual who was born with ambiguously female genitalia but whose genotype is XY).
I believe that we will see women receive the priesthood sometime in my lifetime. There are already ordinances in the temple which are performed by women holding the priesthood (this has been the case since the beginning, but it isn't talked about much). The washing, anointing, and endowment ordinances also are very clear about husbands and wives being anointed to become "priests and priestesses," which suggests that in the next life women do have the priesthood, and that the current condition (where women do not) is more culturally than doctrinally-based. This would be examples of agitators having a doctrinal leg to stand on, which the adherents of same-sex sealings do not.
But, as you said, living prophets reveal the mind and will of God, and they trump existing doctrine. We shall have to see what the Lord says through His servants on the matter.
4. The logic behind the belief that a spiritual confirmation of the Book of Mormon's authenticity also confirms the legitimacy of the LDS Church (as opposed to legitimacy of another denomination in the Latter-day Saint Movement, another church in general, or no particular church at all)?
You would have to get into a detailed discussion of the history of the Brighamites and various other offshoots to answer that question for some people. For most, the answer to that question is as simple as, if the Book of Mormon is the word of God, then Joseph Smith was a true prophet, and if Joseph Smith was a true prophet, then his living successor is also a true prophet. Yes, there are competing claims about who is his living successor, which is why a personal witness/testimony about the current prophet is important. When I became an LDS missionary, I had received previously a testimony about the Book of Mormon, and I assumed that also covered the veracity of Joseph Smith's claims about what he saw and received. As I came to learn in greater detail about those claims, I could see that for my own peace of mind I would need a second witness that was specific about his mission as a prophet. I resolved that night to ask about it in prayer, and I prayed until I received a confirmation that he was truly a prophet of God. Similarly, I have felt a need to know whether Ezra Taft Benson, Gordon B. Hinckley, and Thomas S. Monson were living prophets, and have sought that confirmation. It has come for me in most cases while listening to them speak in General Conference, when I feel the Spirit testifying to me that what I am hearing is true.
5. Why the the Word of Wisdom is today considered a matter of Temple worthiness, when D&C 89 clearly states that its dietary guidelines are not commandments, but recommendations, and that Joseph Smith regularly drank and served alcohol, even up to the hour of his assassination?
During Brigham Young's day, the doctrine changed. Previously it had been considered to be a word of counsel or word of wisdom to provide guidance on the best way to live, but not to be absolutely necessary to follow. The short answer is that when God's prophet said that it was now a commandment, it became one. Similarly, clarifications about what "hot drinks" means have been made by prophetic pronouncement, and although there is no mention of harmful drugs in Section 89, living prophets have also clarified that they are prohibited.
5. Why only certain parts of D&C 89 are taken seriously, while others, such as those discouraging consumption of meat (except during winter or famines), are largely ignored?
Good question! A lot of good health advice is ignored. The parts that were specified as being commandments are now taken very seriously (for example, you can't enter the temples if you are in violation of them). The parts about what grains to eat, eating fruits and vegetables when they are in season, and using meat sparingly are not taken as commandments. I know members (including my wife's family) who take those parts very very seriously, but they are a minority. My wife brings them up often, and does her best to follow them despite my penchant for eating meat.
6. What a "Son of Perdition" is?
a) Anyone who followed Satan in the war in heaven and was cast out of God's presence for rebellion. They were not allowed to be born and receive a mortal body. They are here on earth and are still attempting to win souls to their master's side. After the final judgment, they will be cast into outer darkness. These are the souls that are truly damned in the traditional sense of the term--they go to what traditional Christians think of as hell.
b) Although it is very rare and difficult to achieve, a few souls who are born in this life will be joining Satan's minions in outer darkness. To do so, they must commit a sin worse than murder, which is to "deny the Holy Ghost." That seems like a simple term, but it is more than just saying, "I deny you" or something like that. Most of us do not have the level of knowledge necessary to commit such as sin--the majority of God's children are in partial ignorance of the reality of the Father, Son, and Holy Ghost. St. Peter, for example, denied knowing Jesus three times on the eve of Christ's death, but his sin did not even come close to meriting (if you want to call it that) eternal damnation as a Son of Perdition. It has been said that in order to qualify for that dishonor, you must, in effect, be able to look at the sun and deny its existence, or the equivalent in spiritual terms. This means that knowing fully who Jesus is, having received a perfect and unmistakable witness of His divinity, you must still consent to His death, wishing to join those who drove the nails into his hands and feet and jeered at Him at the cross. Fortunately for those who were actually present at that day, they did not know what they were doing--they had received no witness from the Holy Ghost that it was God the Son that they were crucifying. If they had known, they surely would have stopped and begged His forgiveness. Jesus knew that he could say too much and stop his death, which is why he was so cryptic and close-mouthed with Pilate and his accusers. He also knew that his death was absolutely necessary, and He freely forgave those who ignorantly took part in his deicide. He asked at the end, "Father, forgive them, for they know not what they do."
Those crucifiers did not qualify to be Sons of Perdition, and neither do you nor I nor most of God's children. There will be a few, however, who will be cast out with Satan and the spirits who followed him, and spend the rest of eternity in outer darkness.
