Didache

When you have time and interest, consider reading the Didache, or "The Teachings of the Twelve Apostles". It can be considered to be Christianity's first Catechism. Scholars differ on when it was written: some date it as early as 40-70 AD, others as late as the 4th century. Consensus seems to be emerging for a 70-100 AD date range. What we do know definitively is that it was referred to many times in the writings of early theologians, but the actual text was unknown until the late 1800s, when a copy was reported by the Greek Orthodox church.

It isn't that long, and a number of translations are available online. I've found it to be an interesting source of what the earliest Christians believed. Among other things, it is interesting that at the time this was written, Holy Communion was already referred to as Eucharist (Chapter 9), and there was already a practice of formal confession of sins (Chapter 4). Considering that this writing could very well pre-date some of the books of the Bible, it bears thinking on.