Hebrews 6:17, “So when God desired to show more convincingly to the heirs of the promise the unchangeable character of his purpose, he guaranteed it with an oath,”
One of the main reasons the book of Hebrews was written was to encourage the readers to persevere in their faith so that they would receive all of the promises of God. The author encourages his readers in their faith, reminding them that one of the greatest old covenant saints, Abraham, also had to wait and persevere in obedience before he obtained the promise (6:15).
God was content not only to offer a promise to Abraham and his descendants but also to confirm His promise by means of an oath (6:14). At this point we might ask ourselves why God would need to swear an oath to us. Men swear oaths to each other because we often lie or do not follow through with our promises. But this is not true of God. There is no shadow of deceit in Him (Num. 23:19). He is faithful and always true to His word.
Quite simply, God did not need to make such an oath. As Hebrews 6:17 tells us, He “desired to show more convincingly” the immutability of His purpose to all the heirs of the promise. This is why He made the oath to Abraham. Here we see a marvelous example of God’s condescension to human needs. Our sinful nature makes us so prone to doubt God’s promises. Abraham should have known better than to doubt God’s truthfulness — we also should know better. But sometimes our sin causes us to act as if God’s word cannot be trusted.
Instead of leaving us in our doubt, God’s mercy and love leads Him not only to promise blessing to Abraham, but also to swear it. John Calvin writes: “See how kindly God as a gracious Father accommodates himself to our slowness to believe; as he sees that we rest not on his simple word, that he might more fully impress it on our hearts he adds an oath.” In His love, God decided not to leave us doubting, but to confirm His promise to us with a solemn oath. This is a pure act of grace, He did not have to do this. It is an exercise of His sovereign will, which, as John Owen writes, “is the sole spring of all the grace, mercy and consolation that believers partake of in this world.”
Note finally that the promise to bless and multiply Abraham’s offspring is made not only to Abraham but also to his heirs. We, too, are the heirs of this promise (Gal. 3:29), and God has sworn to bless and multiply His people even in our own day.
The promise to Abraham contains an inheritance in a better country, faithful descendants, and salvation. God confirmed that these would all be granted when He swore an oath to Abraham. Thank God for His love that motivated His swearing of this oath, and for the fact that in Christ, you are promised the same things as Abraham.