Here's an accessible reference that aids personal Bible study or Sunday school preparation: The Layman's Bible Commentary. Volume 5 covers Psalms through Song of Songs, and gives you section-by-section commentary on the flow and theme of each book, as well as historical and literary context for each. Major interpretations are presented for controversial passages and topics. Puzzling passages and Bible practices are explained, and charts and diagrams further aid your understanding. "Take Home" segments provide a practical application for each passage.