Bible calls them men of faith. Where? I've never heard it claimed that everyone in the Bible is without sin.
Did I say without sin? No. I said that some of them didn't have 100% certainty some times. I don't equate that to sin.
In one passage you find David telling his assistant in battle "come, let's cross to the other side, maybe God will give us a miracle". I don't understand the relevance to the conversation.
David is called by the bible "A man according to God's heart". And in this passage he's saying "maybe God will give us a miracle". Maybe is exactly the not 100% I'm talking about.
About wavering, I don't necessarily agree it means doubting. It's different to do something you are not 100% sure about than not doing it because you aren't sure about it.
But without faith it is impossible to please him: for he that cometh to God must believe that he is, and that he is a rewarder of them that diligently seek him. You cannot get into heaven without believing in God. Personally, although the Bible doesn't say it in this passage, I think that you cannot truly believe something that you doubt.
That passage says without faith. Doesn't say without super super certain faith. My point is about the nature of the required faith, not about faith being required. That passage says you need to believe that he is and that he rewards. You can believe that in many degrees.
About the Romans 14 passage he's saying we shouldn't do things without faith / in good conscience. Specifically, the reference to eating is about conscience issues like the eating kosher required or not that was being discussed during Paul's time. Paul's position was that it wasn't a sin for a jewish christian to eat not kosher food, unless he had conscience issues about it. He's not talking about salvation/damnation or anything like. The sin of eating in bad conscience cannot affect salvation in the biblical system, specially in the context of Romans. By that point in the book Paul has event talked about how a christian can be in a crisis of sin and still take comfort that Jesus is his savior (Romans 7 & 8).
About the Thomas Aquinas quote, yes, he is making that distinction. He's not the bible. My point isn't that no religious sources talk about 100% certainty required for such and such thing, but that some do, some don't, and that there are degrees to this.