John 8:56

Jesus was, of course, referring to Abraham as the physical ancestor of His hearers, not their spiritual father. The occasion of Abraham’s rejoicing, to which Jesus referred, is unclear. The commentators have suggested various incidents in his life that Moses recorded (i.e., Genesis 12:2-3; Genesis 15:17-21; Genesis 17:17; Genesis 21:6; Genesis 22:5-14). I think the most likely possibility is Genesis 12:3, the prediction that God would bless the whole world through Abraham. In any case, Jesus said that Abraham anticipated His day. Jesus was claiming that He fulfilled what Abraham looked forward to. We need to be careful not to read back into Abraham’s understanding of the future what we know from revelation that God gave after Abraham died. Clearly Abraham did know that his seed would become the channel of God’s blessing to the entire world.

The Hebrew and Greek words translated "seed" (Heb. zera, Gr. sperma) are collective singulars, as is the English word. It is not clear from the word whether one or more seeds are in view. The Bible uses the phrase "seed of Abraham" to refer to four entities: Jesus Christ (Galatians 3:16), Abraham’s spiritual children (believers, Galatians 4:6-9; Galatians 4:29), his physical descendents (the Jews, Genesis 12:1-3; Genesis 12:7; et al.), and his physical and spiritual posterity (saved Jews, Romans 9:6; Romans 9:8; Galatians 6:16).