The first time we see an altar in the Bible is after the flood (Gen.8:20). The second Pentecost, the first was on day four of Creation. But the altar was built to support the act of sacrifice which had already been in the earth before the flood: we must backtrack to Genesis 4:26 which says, “And to Seth, to him also there was born a son; and he called his name Enos: then began men to call upon the name of the LORD.” The phrase “then began men to call upon the name of the LORD” must be understood as the act of sacrifice. Rewinding to the original act of sacrifice we find that God made coats of skins and clothed Adam and Eve after they had fallen. The word “make” is the word “Asah” which also means to sacrifice. God couldn’t make sacrifice for mankind until He called unto them: Genesis 3:8-9 says, “And they heard the voice of the LORD God walking in the garden in the cool of the day: and Adam and his wife hid themselves from the presence of the LORD God amongst the trees of the garden. And the LORD God called unto Adam, and said unto him, Where art thou?” You called unto God because He called unto you first! It is the altar of Christ which was foreordained before the foundation of the world and manifested in time that continues to call us to himself. You have not chosen me, but I have chosen you! Christ is calling us to an altar, the cross.
-Anthony D. Booker