Here again we find the Lord Jesus Christ (Genesis 22:16-18). The Angel of the Lord who speaks here is my Lord Jesus Christ. In this passage the most blessed Trinity, God the Father, Son, and Holy Spirit, swears an oath. The words are conveyed by my Lord Jesus Christ, who swears the oath by Himself and His heavenly Father and the Holy Spirit. Hence He is called the “Angel (or Messenger) of the LORD,” for He is God the Father’s ambassador to mankind, always reporting to us on behalf of the Father and revealing the Father’s disposition toward us (John 1:18). Thus He says, “‘I have sworn by Myself,’ says the LORD. Hear, O Abraham, these are not the words of a mere angel, but they are the words of the Lord. The Lord Jehovah, the true God, the most blessed Trinity, is now dealing with you. I, Jesus, the Angel of the Covenant, convey the words, but My Father and the Holy Spirit speak in one accord with Me. Hear, O Abraham, the everlasting God’s unanimous judgment regarding Your salvation.” And in such manner the Lord Jesus went on to describe how He Himself was the Seed of Abraham through whom all the nations of the earth would be blessed. With devout hearts, then, let us now meditate on all these things.
O dearest Lord Jesus Christ, how solemn and strong is the precious oath that You established here! You swore by Yourself, for You could not swear by any greater, as men do (Heb. 6:16). You are of equal majesty, glory, and honor with the Father and the Holy Spirit, wherefore You swore by Your right hand, by the arm of Your power (Is. 62:8). You swore by Your great name (Jer. 44:26). You swore by Your holiness (Amos 4:2). You swore by Your soul (6:8). You swore a double oath by Your truth: “Truly, Truly,” (John 3:3), which is to say, You swore by Yourself, for You are the Truth (John 14:6; 17:17). You gave Your eternal, omnipotent, true, holy, changeless Godhead as a pledge for Abraham and for us believing hearts. As certainly and truly as You are God from eternity, so certainly and truly shall Your pledge hold true that we will be saved by You. You would rather forfeit Your eternal Godhead and almighty power than allow us believing hearts to be betrayed. Oh, how high You have kept our hope against all tribulation! You remain God forever, so Your words shall remain true forever too, for “it is impossible for God to lie” (Heb. 6:18).
Behold, dear heart, here is the first oath that God swears in Holy Scripture. Above in Genesis 21 Abimelech and Abraham exchanged oaths, but we have never read anything about God doing so until now. Oh, how comforting this is! God’s first oath was not to swear in His wrath that we would not enter His rest, as in Psalm 95:11, but to assure us of the hope in Jesus Christ would be blessed and saved. This is why Augustine says, “The Lord God had often promised but never sworn. Yet what is the oath of the true and reliable God if not a confirmation of the promise and a rebuke of unbelievers?” (The City of God, bk. 16, ch. 32.)
Valerius Herberger The Great Works of God: Parts Three and Four: The Mysteries of Christ in the Book of Genesis, Chapters 16-50 113-114