I believe this is how Jesus was able to be born from the line of Abraham. Abraham was willing to sacrifice his only son. Since Ishmael & his mother Hagar were sent away, Isaac was Abraham's only son & only lineage left to him. Instead of God destroying this only lineage. He spares the life of Isaac. Later on we see that, yes, "God will provide himself a lamb for a burnt offering." That lamb referenced in Gen 22:8 is Jesus. God will later sacrifice not a son of man, but His only begotten son, which is THE SON of MAN.