The Promise that GOD makes is the Promise Revealed. That’s why we live by Faith and not by sight. GOD has ready fulfilled His Promise; we just have to catch up to the time that the Promise is revealed.
His Promise is His Will, they are separate but one. The Will and Promise are what GOD has giving to us, but we must have faith in the Promise because He will reveal His Glory in the process of time. GOD is not a man that He should lie.
Understand this, GOD can not lie. There is so much power in Him that His words will come to pass. The Birth of Christ is the Promise Revealed. Christ and Him Crucified is the object of our Faith. When GOD says He will, He did. When GOD says He promises, He revealed.