Faith based theology, or not
Some books in the New Testament go on and on about "faith", and others don't. This is an important difference. If you keep the questions of "how important is faith, and how does it relate to salvation and works?" in mind, and read the New Testament and post-NT Christian writings, there is a noticeable divide. The differences become very profound: Some books do not use the word faith once, and other books go on and on about it.
In general books can be fairly easily categorised into two categories regarding the importance, or lack of importance, that they give to "faith". Some books talk about salvation, judgement, eternal life and don't mention faith even once, while other books talk as though faith is absolutely essential and necessary with regard to all these topics. This demands an explanation.
I can see two possibilities to explain this:
1) That there was a massive theological divide within early Christianity, one side of which saw "faith" as being central, the other side of which were not interested in faith and considered it unimportant and were interested only in good works.
2) That there was no massive theological divide within early Christianity, and both sides are simply using different words to express essentially the same concepts.
Which is the case? All the reasons seem to favor (2) over (1), three reasons:
(a) We have no real evidence of massive theological differences to the degree that hypothesis (1) would require.
(b) Despite the differences in use of the word "faith", both sides consistently depict a works-based judgement.
(c) Most Christians would be extremely relunctant to think that different writers of the NT were in opposition to each other theologically.
Whichever hypothesis we accept the consequences are severe:
If we accept (1), then we are faced with the fact that New Testament Christianity was composed of two opposing theological views, and we have to choose one to believe. We can either choose to believe in the importance of faith, or in the importance of works, and either way we will be implicitly accepting some books of the NT and rejecting others. We have to stop kidding ourselves into thinking that we "just believe the NT" and admit that we have arbitrarily picked one of two NT views.
If we accept (2), then we are faced with the fact that everything that is meant by the word "faith" can be translated into language that deals with good works without significant loss of meaning. ie, we'd have to say that faith and works are in some way identical. Whatever our theology was regarding faith, it would have to be able to be translated into language that didn't use the word "faith". We'd have to say that the books which didn't use the word faith and instead only talked about works-based salvation were not at all wrong, and were an equally valid way of expressing the same concept.