Titus 1:1

Here is the preface to the epistle, showing, I. The writer. Paul, a Gentile name taken by the apostle of the Gentiles, Act 13:9, Act 13:46, Act 13:47. Ministers will accommodate even smaller matters, so that they may be any furthering of acceptance in their work. When the Jews rejected the gospel, and the Gentiles received it, we read no more of this apostle by his Jewish name Saul, but by his Roman one, Paul. A servant of God, and an apostle of Jesus Christ. Here he is described by his relation and office: A servant of God, not in the general sense only, as a man and a Christian, but especially as a minister, serving God in the gospel of his Son, Rom 1:9. This is a high honour; it is the glory of angels that they are ministering spirits, and sent forth to minister for those who shall be heirs of salvation, Heb 1:14. Paul is described more especially as a chief minister, an apostle of Jesus Christ; one who had seen the Lord, and was immediately called and commissioned by him, and had his doctrine from him. Observe, The highest officers in the church are but servants. (Much divinity and devotion are comprehended in the inscriptions of the epistles.) The apostles of Jesus Christ, who were employed to spread and propagate his religion, were therein also the servants of God; they did not set up any thing inconsistent with the truths and duties of natural religion.

— Matthew Henry's Concise Commentary (public domain)