The epistles are basically letters that were written to the church. They provide doctrine, guidelines and principles for the church to follow. The epistles are written specifically to the church, that is to us, if we are in Christ.
The epistles explain who we are in Christ and our relationship to God. The church is unique and God refers to believers as His children, as the body of Christ and He says that we are joint heirs with Christ. The epistles are wonderful books that reveal that we are complete in Christ, that we have all things that pertain to life and godliness, that we can do all things through Christ who strengthens us, and much more.
The book of Acts is a book of history revealing the beginning of the church. The church is compiled of "Born again" believers and is under grace. It is different from the Old Testament nation of Israel.
The epistles consist of the following books of the Bible; Romans, 1 & 2Corinthians, Galatians, Ephesians, Philippians, Colossians, 1 & 2Thessalonians, 1 & 2Timothy, Titus, Philemon, James, 1 & 2Peter, 1, 2 & 3John, Jude. Hebrews is written to Jewish Christians.