Hebrews 6:16,17

Heb. 6:16-17. For men verily swear by the greater: and an oath for confirmation (is) to them an end of all strife. Wherein God, willing more abundantly to shew unto the heirs of promise the immutability of his counsel, confirmed (it) by an oath:

Here is further evidence of an important argument in Edwards's greatest work, Freedom of the Will, showing "it to be impossible that Christ should not have persevered in perfect holiness."

4. All the promises which were made to the Church of old, of the Messiah as a future Saviour, from that made to our first parents in paradise, to that which was delivered by the prophet Malachi, show it to be impossible that Christ should not have persevered in perfect holiness. The ancient predictions given to God's church of the Messiah as a Saviour, were of the nature of promises; as is evident by the predictions themselves, and the manner of delivering them. But they are expressly, and very often called promises in the New Testament; as in Luke 1:54; Luke 1:55; Luke 1:72; Luke 1:73; Acts 13:32; Acts 13:33; Romans 1:1-3; and chap. Romans 15:8; Hebrews 6:13, etc. These promises were often made with great solemnity, and confirmed with an oath; as in Genesis 22:16; Genesis 22:17, "By myself have I sworn, saith the Lord, that in blessing, I will bless thee, and in multiplying, I will multiply thy seed, as the stars of heaven, and as the sand which is upon the sea shore:… and in thy seed shall all the nations of the earth be blessed." Compare Luke 1:72; Luke 1:73, and Galatians 3:8; Galatians 3:15; Galatians 3:16. The Apostle in Hebrews 6:17; Hebrews 6:18 speaking of this promise to Abraham, says, "Wherein God willing more abundantly to shew to the heirs of promise the immutability of his counsel, confirmed it by an oath; that by two immutable things, in which it was impossible for God to lie, we might have strong consolation." In which words, the necessity of the accomplishment, or (which is the same thing) the impossibility of the contrary, is fully declared. So God confirmed the promise of the great salvation of the Messiah, made to David, by an oath (Psalms 89:3; Psalms 89:4), "I have made a covenant with my chosen, I have sworn unto David my servant; thy seed will I establish forever, and build up thy throne to all generations." There is nothing that is so abundantly set forth in Scripture, as sure and irrefragable, as this promise and oath to David. See Psalms 89:34-36; 2 Samuel 23:5; Isaiah 55:3; Acts 2:29; Acts 2:30; Acts 13:34. The Scripture expressly speaks of it as utterly impossible that this promise and oath to David, concerning the everlasting dominion of the Messiah of his seed, should fail. Jeremiah 33:15, etc.: "In those days, and at that time, I will cause the Branch of Righteousness to grow up unto David…. For thus saith the Lord, David shall never want a man to sit upon the throne of the house of Israel." Verse Jeremiah 33:20-21: "If you can break my covenant of the day, and my covenant of the night, and that there should not be day and night in their season; then may also my covenant be broken with David my servant, that he should not have a son to reign upon his throne." So in verse Jeremiah 33:25-26. Thus abundant is the Scripture in representing how impossible it was, that the promises made of old concerning the great salvation and kingdom of the Messiah should fail: which implies, that it was impossible that this Messiah, the second Adam, the promised seed of Abraham, and of David, should fall from his integrity, as the first Adam did.

The text also appears in the second greatest work, Religious Affections, showing that the covenant gives saints "an undoubting hope and full joy in an assurance of their future glory."

And the nature of the covenant of grace, and God's declared ends in the appointment and constitution of things in that covenant, do plainly show it to be God's design to make ample provision for the saints having an assured hope of eternal life, while living here upon earth. For so are all things ordered and contrived in that covenant, that every thing might be made sure on God's part. The covenant is ordered in all things and sure: the promises are most full, and very often repeated, and various ways exhibited; and there are many witnesses, and many seals; and God has confirmed his promises with an oath. And God's declared design in all this is, that the heirs of the promises might have an undoubting hope and full joy, in an assurance of their future glory. "Wherein God, willing more abundantly to show unto the heirs of promise the immutability of his counsel, confirmed it by an oath; that by two immutable things, in which it was impossible for God to lie, we might have a strong consolation, who have fled for refuge, to lay hold on the hope set before us" (Hebrews 6:17-18). But all this would be in vain, to any such purpose, as the saints' strong consolation, and hope of their obtaining future glory, if their interest in those sure promises in ordinary cases was not attainable. For God's promises and oaths, let them be as sure as they will, can't give strong hope and comfort to any particular person, any further than he can know that those promises are made to him. And in vain is provision made in Jesus Christ, that believers might be perfect as pertaining to the conscience, as is signified (Hebrews 9:9), if assurance of freedom from the guilt of sin is not attainable.