Most New Testament books are letters (Greek epistolé), written primarily to church congregations by Paul, James, Peter, John, and Jude, though a few go to individuals such as Timothy, Titus, Philemon, and Gaius. Hebrews is technically a treatise, a systematic argument with a letter-like conclusion. A typical first-century letter followed a strict format: the writer's name, the recipients, a greeting, the body, and closing greetings, perhaps with a date. Parenthetic remarks about the recipients are common (I Peter 1:2), and extra material sometimes attaches to the salutation (II Peter 1:3-4). The greetings are nearly uniform, as in Romans 1:7: "Grace to you and peace from God our Father and the Lord Jesus Christ," sometimes with mercy added. James writes a simple "Greetings," Peter multiplies grace and peace, II John and Jude give longer greetings, III John is terse but kind, and I John omits the greeting, which suggests it is not technically an epistle. The most significant feature is that none of the twenty epistles from five apostles sends greetings from the Holy Spirit. Only the Father and the Son send grace, mercy, and peace, because there is no Third Person in the God family. The Spirit is the divine essence, mind, and power of the Father and the Son, by which They live in believers and unite them with Themselves, as John 14, John 17:20-23, and II Corinthians 3:17 show.