Question: What few books would you recommend as a foundation for understanding the NT?
The foundation for understanding the NT is at one level prayer, humility, and openness to what the living God may be saying in Jesus Christ and the power of the Holy Spirit. At another level, very closely integrated with this first one through the fact of the incarnation, the foundation is of course the knowledge of the history, culture and language of the time, i.e. NT Greek, a knowledge of the Jewish world of late antiquity, and the wider Greco-Roman context. This doesn’t mean you have to be an ancient historian before you can understand the NT, but it is vital that those who are teaching in the church base their readings on real historical understanding rather than anachronistic assumptions.
I wrote my book The New Testament and the People of God precisely in order to address this need among my own students. This was what I wanted them to know before they began; I found in tutorials and seminars I was constantly having to go through these basics rather than the topic set because otherwise they were making the wrong assumptions about what words and ideas meant, etc.
I actually still find that the big reference books, especially The Oxford History of the Christian Church and The Oxford Classical Dictionary, are invaluable on an almost daily basis. The basic introduction by Achtemeier, Green and Thompson is excellent for those starting out. The Eerdmans Dictionary of the Bible is very good. But actually I would urge anyone who wants to get into the NT seriously to learn as much of it by heart as they can. If in Greek so much the better. Talk whole chapters and books on to cassette tape and play them in the car, when doing housework, etc etc. There is no substitute for a ready, easy familiarity with the text itself. Apart from anything else, learning whole passages rescues you from the out-of-context readings that so bedevil an early attempt to understand scripture.