Prophecy which reaches its fulfillment before the time-period of the cross is understood in the literal sense. If a prophecy speaks of the descendants of Abraham before the time-period of the cross, then is identifying the literal blood descendants of Abraham.
After the time-period of the cross prophecy is understood in the spiritual sense. The descendants of Abraham after the time-period of the cross are descendants of Abraham that are connected to Abraham by faith, not blood.
Howbeit that was not first which is spiritual, but that which is natural; and afterward that which is spiritual. 1 Corinthians 15:46.
And if ye be Christ’s, then are ye Abraham’s seed, and heirs according to the promise. Galatians 3:29.
For he is not a Jew, which is one outwardly; neither is that circumcision, which is outward in the flesh: But he is a Jew, which is one inwardly; and circumcision is that of the heart, in the spirit, and not in the letter; whose praise is not of men, but of God. Romans 2:28, 29.
This is “replacement theology”, unfortunately condemned by the vast majority of Christendom today.