John the Baptist's reference to Jesus as the Lamb of God seems to point to sacrifice because of the lamb's use throughout the Old Testament. The first sacrifice we read of is a lamb- the first of Abel's flock, which was pleasing to God. Leviticus tells repeatedly of a lamb to be slaughtered (i.e. Leviticus 4:32-35). Exodus, especially, speaks of the Passover lamb whose blood covered the doorpost, and when it was seen by the Angel, the firstborn (and the whole family, consequently) was spared. I think.