Questions: (second question is below)
1. Out of 500 billion galaxies we can’t be the only life in the universe and how does that affect mankind and a savior?
Answer: First of all, this question based on an improvable assumption. Why, logically, is it seemingly impossible that the earth could contain the only life in the universe? If we assume that life came about by completely random accidental processes, then the premise seems reasonable. If life is a natural result of natural processes, then one can reasonably conclude that PROBABLY there is life elsewhere, as the probability of the correct conditions and sufficient luck happening only in one placed seems remote (but not zero). However, to assume that life came about by random accident is to assume the answer before asking the question. The question is that of origins. The broad question is the creation of life by God. If we assume that God did not create life and then use that conclusion to prove that God did not create life, then this is clearly a circular argument. If we do NOT assume that God did not create life (ie if we accept the possibility that God did create life) then your premise is a false one.
So… it is simply not true that we can’t be the only life in the universe. However, this brings up a second question. Are we, in fact, the only life in the universe? The answer is that neither the Bible nor science has any information whatsoever to offer on this one. There is literally zero scientific evidence of life outside our solar system (not that this proves there is no life, but that there is no evidence for that life so far). There is also literally zero biblical evidence for life outside our solar system. Therefore, if we are honest, we will have to admit that we simply do not know if there is life elsewhere.
This brings us to the last question you raise. Let us go ahead and make the unfounded assumption, for the sake of argument, that there is no life elsewhere in the universe? What does that say about God and about us? It is not uncommon for people to feel that it is ridiculous for there to be such an unimaginably vast universe with life (and more importantly sentient life) in only one place. (Remember that this is only a premise and an unproved one at that). This feeling, however, is not logical. The idea that there “has” to be life elsewhere because the universe is so big is a logical fallacy. This is what is known as the logical fallacy of size. The assumption behind this is that something very big is more significant than something small. If the universe is fantastically large and “we” are fantastically small, the emotional (but not logical) conclusion is that we are very insignificant. Are smaller people less significant than larger people? Is a $100 bill of less value because it weighs less than a quarter? Is a human less significant than an elephant because it is smaller? Is the earth less significant than Jupiter because it is smaller? Size has NOTHING to do with importance or significance. Therefore, if God chose to create an unimaginably vast universe in order to create humans to love and have a relationship with them, how is that a logical problem? God is obviously not affected in the least by distance and time. A universe which is unimaginably big and which has been around for an unimaginably long time may be difficult for us limited humans to grasp, but this is not the slightest problem for the infinite God.
In the end, the question you ask is really an emotional one, but logically, there is no difference whatsoever on the meaning of the gospel and of God creating us based on the size of the universe.
2. Why in the OT did men have many wives and this was ok and now it would be adultery and seen as philandering.
Answer: It was never “OK” for men to have many wives. God has never approved of this. Nowhere in the Bible does it even remotely suggest that God wanted anyone to have multiple wives. The Bible, being accurate history, of course, reports the existence of multiple wives, even among the Jews. However, there is no evidence that he was happy about this. There is the doctrine of progressive revelation, which means that over time, God revealed his will more precisely to his people. The Old Covenant was given to a more primitive people and God made allowance for their sin. For example, he allowed the men to divorce their wives, but Jesus is very specific about this. He tells us that God allowed this because of the hardness of their hearts (Mark 10:5). In other words, although God clearly has always hated divorce, in the cultural setting of the Jews in the time of Moses, he allowed the Jews (many of whom really had little if any faith in God) to divorce their wives, but God never approved of this practice. The same applies to taking multiple wives. God has never approved this, but he did allow it. Actually, there is no provision anywhere in the Old Testament for multiple wives. Technically, this was never allowed by God, but there was no specific provision making it illegal.
Another point to be made is that the examples of multiple wives in the Old Testament all have the identical message: It is a total disaster. Abraham had two wives and it was a disaster. Solomon had many wives and it was a total disaster. David has several wives and it completely destroyed his family. I would challenge anyone to prove from the Bible that God approves of multiple wives. It is worth noting that actually the New Testament does not specifically absolutely condemn a man having more than one wife. That is interesting. All Christians I know of agree that God wants one man to marry one woman. This is so obvious from Ephesians 5, Genesis 2 and many other place, but it is worth noting that polygamy is not expressly forbidden in the New Testament. Let me speculate as to why. I happen to know of a situation in Nigeria where a man with three wives was converted to Christianity. What is he to do? Does he divorce two of them? Which two? What would be the result for the two divorced? Would sex with the third be adultery since he had divorced the other two? There is no logical solution to this problem. This man was allowed by the church to keep his three wives, but obviously the church would never perform a plural marriage.
The answer is that it was never “OK” for a man to have more than one wife, but it appears that God has tolerated this because of the situation in the world and because of our hardness of heart.