Abraham's Explanation

Apostle John who was with Christ until his last moment of the crucifixion, has revealed that Jesus Christ is not the image of Word alone, but the Image of Father, Word and the Holy Spirit, and we must believe in him to overcome this world - 5.Who is it that overcomes the world? Only the one who believes that Jesus is the Son of God. 6.This is the one who came by water and blood—Jesus Christ. He did not come by water only, but by water and blood. And it is the Spirit who testifies, because the Spirit is the truth - 1 John 5:5-6

To understand this in a better way, apostle John first explaining the Trinity of our Heavenly Father as Father, Word and Holy Spirit - because there are three who are testifying in Heaven: the Father, the Word, and the Holy Spirit, and these three are one -  1 John 5:7

And then he explained about the Son Jesus Christ, that Jesus had all three of them(Father, Son, and the Holy Spirit) in him - and there are three who are testifying in the earth: the Spirit(Holy Spirit), and the water(Word), and the blood(Father) and the three are into the one(Jesus Christ) - 1 John 5:8

That was the reason Apostle Paul is saying that Jesus Christ is the Image of the invisible God - The Son is the image of the invisible God, the firstborn over all creation - Colossians 1:15 that means in Jesus Christ we can see the Son (The Word became flesh - John 1:14), and our Heavenly Father (Whoever has seen me has seen the Father - John 14:9), and the Holy Spirit (The Spirit of the Lord is upon me - Luke 4:18).

Abraham's Explanation

The Bible says that, Abraham built three Alters, but no mention of the offerings on these Altars.

Altar #1: Abram passed through the land to the place at Shechem, to the oak of Moreh. At that time, the Canaanites were in the land. Then the Lord appeared to Abram and said, To your offspring I will give this land. So he built there an altar to the Lord, who had appeared to him - Gen 12:6-7

Altar #2: From there he moved to the hill country on the east of Bethel and pitched his tent, with Bethel on the west and Ai on the east. And there he built an altar to the Lord and called upon the name of the Lord - Gen 12:8

Altar #3: So Abram moved his tent and came and settled by the oaks of Mamre, which are at Hebron and there he built an altar to the Lord - Gen 13:18

But when offering time comes, God asked Abraham to bring (מְשֻׁלָּ֑שׁ) shaw-lash of three animals - So He said to him, Bring Me a מְשֻׁלֶּ֔שֶׁת (shaw-lash) of heifer, a מְשֻׁלֶּ֔שֶׁת (shaw-lash) of female goat, מְשֻׁלָּ֑שׁ (shaw-lash) of ram, a turtledove and a young pigeon - Genesis 15:9

Shaw-lash means one third portion, the same word shaw-lash has been used for dividing the land into three pieces - You shall prepare roads for yourself, and divide into three parts (shaw-lash) the territory of your land which the Lord your God is giving you to inherit, that any manslayer may flee there - Deuteronomy 19:3 

So, Abraham brought one third portion from a heifer, one third portion from a female goat, and one third portion from a ram and offered to the God, In weight what Abraham offered is equivalent to one whole sacrificial animal, but actually its taken from three different sacrificial animal, Like that our Lord Jesus Christ, the one crucified for our salvation is from the God of Trinity(Father, Word, and Holy Spirit) - 10.And he brought him all these, cut them in half, and laid each half over against the other. But he did not cut the birds in half. 11.And when birds of prey came down on the carcasses, Abram drove them away - Genesis 15:10-11

That was the reason Apostle Paul is saying, the three sacrificial animals(Goats, Bulls and Heifers) are just a sign for our Lord Jesus Christ - 13.For if the blood of goats and bulls, and the sprinkling of defiled persons with the ashes of a heifer, sanctify for the purification of the flesh, 14.how much more will the blood of Christ, who through the eternal Spirit offered himself without blemish to God, purify our conscience from dead works to serve the living God - Hebrews 9:13-14

And in the same verse, God also asked Abraham to bring dove and young pigeon to explain the father and son relationship between the Trinity God and the Son Jesus Christ, Yet for us there is one God, the Father, from whom are all things and for whom we exist, and one Lord, Jesus Christ, through whom are all things and through whom we exist - 1 Corinthians 8:6