In Hebrews 6:13-20 the author shows why God’s people can rest in the promises of God. God has not only given a promise that cannot be broken in that God cannot lie, but He has also confirmed that promise with an oath. If one only had a promise from God that would be enough to be sure that it will come to pass, however, God, in His grace, gives the promise and then confirms it with an oath so that by two unchangeable things in which it is impossible for God to lie we might be assured that the promises will come to pass.