Okay, I've got to tell you this is one of the more difficult things to deal with in the Bible. Jewish theology takes a very hard-line stance that God does not change, period. (It's actually for this very reason that many Jews reject Christian theology, as they view the incarnation of Christ to be a "changing" of God's essential nature, which is easy to understand.) If God doesn't change, and indeed, even Christians believe that God doesn't change His mind at least, then what does it mean here and in a number of other places that God "repents" of something?
Probably, you have to look at the nature of the word itself. Interestingly enough, in the Hebrew this is a word with the same root that Noah's name comes from, and Noah's name means "rest" or "comfort". Actually, this word is translated most often as either "comfort" or "repent", and slightly more often the former. But enough Hebrew, I need to get to the point, or at least a point. What can we say about a word that can be translated as either "repent" or "comfort"? What do these terms have in common? I think the operative idea behind both senses of the word is "This has gone on long enough, so we will put a stop to it."
On a personal note, I myself have been doing a study of the concept of repentance, both for my personal spiritual walk, and for my understanding of theology. When a person becomes a Christian, theologically it is understood that one's salvation comes from the Lord, and only from the Lord. There is nothing one can do to earn it, one merely accepts it from God. Yet somewhere in the midst of this, there is a call for the believer to repent from sin. Is repenting from sin something one does in order to become a Christian, or is it something one does as a result of becoming a Christian? In either case, even if one has been a Christian for some time, repentance is something one has to deal with over and over, since becoming a Christian does not imply immediate perfection. So what is repentance? Repentance is deciding that the bad situation in one's life has gone on long enough, and it's going to stop. That may be repenting from a life separated from God, or it may be repenting from a particular habitual sin. A person probably never made a conscious decision to have habitual sin, nor did they purposefully separate themself from God, but they decide it's time to do something about it.
Here, God is looking at the world He created, and He's saying, "Alright, this has gone on long enough. The world is now so much of an evil place that something needs to be done, and I will comfort the good men of this world by ending the existence of the bad men." And I think, but I can't say for sure without reading through the list, that that's what God means whenever He "repents": that He is going to stop something from continuing.
The SAB goes onto say that the flood as a very concept is "cruel and violent". I actually agree. This is one of the first of many times in the Bible that God does something that I find quite shocking. The real question in the end is whether such an act was warranted. I think verse 5 was trying to hint at that, that evil had reached epidemic proportions, and there was really nothing left to do.
Was Noah perfect, though? The SAB quotes the KJV as saying "Noah was a just man and perfect." However, this is somewhat of a misquote. The KJV does not have a period there, and the rest of the sentence is important in two ways. The full sentence: "Noah was a just man and perfect in his generations, and Noah walked with God."
What does "...perfect in his generations..." mean? Here's a thought I have heard that makes sense in light of yesterday's post: Noah had a clear genealogy going back to Adam that didn't include any Nephilim. One of the things that God may have been trying to do is rid the world of the polluted genetic material of these "giants", and Noah, as well as being a pretty good guy, was also someone whose family was 100% human. It may have simply meant that he was a good guy in comparison to everyone else in the world, too.
I think the thing that really sets Noah apart is that he "walked with God" however. It seems pretty clear from the Bible as a whole that the thing God esteems most in a person is their devotion to Him. Noah is a person who wants to do right in the eyes of the Lord, so he spends time devoted to Him. That's what really makes him the right person for the job.
Final note before I wrap this up: I don't think Shem, Ham, and Japheth are triplets, and I've heard it suggested that in fact they may not have been born in that order, either, but were listed according to the importance of their descendants, Shem being the father of the Middle Eastern people, including the Jews, Ham being the father of the Canaanites, whose land eventually becomes Israel, and Japheth, whose descendants don't play a big role in the events of the O.T.