either one of the better Bible dictionaries (see II.5.5.1) or the introduction to one of the better commentaries (see IV.13.3); if you have time, interest, and available resources (a good library nearby), you may pursue some of these matters further through the bibliography provided in the dictionary article. Beyond that, you also need to familiarize yourself with the nature and composition of the church(es) to which the epistle was written. Are they chiefly Jewish Christians, Gentiles, or some mixture?