God provides a model of the saving work of His Son who will take on a fully human nature through a descendant of Abraham. Notice the details: Isaac is Abraham’s son, only son, and beloved (see John 3:16). They go to Mt. Moriah, which is where Solomon’s temple will be built and near the place of Jesus’ crucifixion. Isaac carried the wood for the fire as Jesus carried His cross. Abraham tells the servants that he will return with Isaac (see Hebrews 11:17-19). God Himself provided the ram for the sacrifice—the substitute for Isaac.
Abraham took a third wife and had five more children. So, who are the children of Abraham? Not any of the seven born according to the flesh, but only Isaac according to the promise, indicative of the regenerate soul, the “Israel of God” (see John 3, Romans 2:28-29, and Galatians 3:29).