The answer is: Ephesians

Ephesians 1:1 - Ephesians, authored by Paul, explores the theme of unity in the church, emphasizing the church as the body of Christ. Notably, it introduces spiritual gifts (Ephesians 4:11-13) and the armor of God (Ephesians 6:10-18). This connection enriches the understanding of the church's role within the New Testament.