The promise includes (1) the increase of descendants—they shall be as countless as the stars in the heavens and as the grains of sand along the shore; (2) authority over adversaries, specifically the Canaanites and their confederates; (3) the outpouring of spiritual blessings to all nations through Abraham’s descendants, particularly as the Apostle clarifies, through one pivotal Descendant, Christ, the Son of God (Galatians 3:16).
On Holy Saturday, the remembrance of Christ the Saviour’s suffering, death, burial, and resurrection is interwoven. This is why one of the services, Vespers, includes a reading pertaining to the sacrifice of Isaac—this act serves as a foreshadowing of Christ’s passion, death, and resurrection. The following parallels can be noted between Isaac's sacrifice and the events it prefigures:
1) Just as Abraham offered his beloved son, Isaac, out of love for God, so God the Father did not withhold His only begotten Son but gave Him up for us all (John 3:16, Romans 8:32). 2) Isaac journeys from his father’s home to the place designated by God for his sacrifice; likewise, Christ is to leave Jerusalem and suffer outside its walls (Hebrews 13:11). 3) Isaac separates from his servants as he ascends the mountain where he is to be sacrificed; similarly, Jesus, abandoned by His disciples, ascends the hill of atonement. 4) Both Moriah, where Isaac’s altar was prepared, and Golgotha, where Christ was crucified, are part of the hills surrounding Jerusalem. 5) Isaac carries the wood for the offering. In parallel, Jesus bears His cross and is ultimately lifted up upon it. 6) Isaac willingly submits to his father for sacrifice. In the same way, Jesus remains fully obedient to His Father’s will throughout His suffering, faithful even unto death, the death of the cross (Philippians 3:8). 7) Isaac is condemned to die unjustly; Jesus suffers and dies for the sins of others, although He is entirely sinless and holy. 8) Isaac’s deliverance from death mirrors Christ, who overcame the grave through His resurrection. 9) While Isaac does not endure real suffering himself, a ram takes his place. Similarly, Christ does not suffer in His divine nature, but only in His humanity, which is typified by the ram. 10) On the third day after the sacrifice, Isaac’s mother witnesses him alive; on the third day, the Church also sees Christ resurrected, as noted by Chrysostom. 11) Isaac's sacrifice results in abundant blessings for all his descendants; likewise, the sacrifice of Jesus Christ brings countless blessings to all who believe in Him, regardless of their lineage or tribe.