I find Colossians 1:15 lets us know Jesus is the image of the Invisible God and he is first born of every creature.
In high school English the English teacher stressed to us that the word ' and ' is a conjunction between two.
So, the word ' and ' at 1 Corinthians 8:6 indicates one God the Father... ' and ' one Lord, Jesus Christ.....
So, to me 1 Corinthians 8:6 is talking about two (2) persons: God ' and ' Jesus.
The person of God whom the resurrected Jesus appeared before Him according to Hebrews 9:24.
Jesus continues to serve as the Word of God, God's spokesman, as per John 12:49-50; John 14:10; John 7:16-17.
Jesus is the Word made flesh. That is God personally wrote out His DNA. His DNA is the Word of God. So I dont' believe He's just a spokesman of God. Any angel or prophet can do that. But Jesus is the testament of God in the flesh. The Word of Life. (1 John 1:1) Jesus is the bread of Life (John 6:35) that gives His flesh for the meat of the world. (John 6:55) That means He gave His body to be broken so we could have life. (Matthew 26:26) So it is written "Taste ye and see that Jehovah is good, Oh the happiness of the man who trusts in Him." (Psalm 34:8)
The thing about Jesus is He is human. So when it says "one Lord" it means His humanity. Which His mission is the restoration of all humanity. He's the prophesied "Son of man" who would deliver the kingdom restored and whole to the Father again. (Daniel 7:13) That's why He came. So God said to a human being "Sit thou at my right hand, until I make thine enemies thy footstool."
So Jesus the human being has been given all power (Matthew 28:18) and sits on the right hand of all power. (Matthew 26:64) He has been given the key of David and His mission is to reconcile all things to the Father again as it says in 2 Corinthians 5:18, or as it says in Colossians 1:20 He is reconciling all things
to Himself. Either way it says the same thing because He is the Father manifest.
2 Corinthians 5:18
And all things are of God, who hath reconciled us to himself by Jesus Christ, and hath given to us the ministry of reconciliation;
Colossians 1:20
And, having made peace through the blood of his cross, by him to reconcile all things unto himself; by him, I say, whether they be things in earth, or things in heaven.
It was necessary that all power be given to the Son of Adam so that the descendants of Adam could be saved through Him. That's why He's the Messiah, the Savior.
That doesn't mean He isn't also God manifest. God will not share His glory with another. Jesus said that the good Shepherd gives His life for the sheep and furthermore Jesus taught that greater love has no one than this, that one lays down his life for his friends. What we could not do for ourselves, God coming in our likeness has done.
So of God we know that He is greatest in love. Because God is love. (1 John 4:8)
And we know that God is the good Shepherd. (Psalm 23)
In conclusion, God had to die to fulfill His great love and that He is the true Shepherd of the sheep. But since God cannot die; God required a human body.
Jesus the Son of God, born of a woman and created flesh and blood was God manifest. He existed before as God (Isaiah 9:6) and His body is created in the womb. His body is the "Lamb of God" the sacrifice for sins. (Hebrews 10:5)
Hebrews 10:5
Wherefore when he cometh into the world, he saith, Sacrifice and offering thou wouldest not,
but a body hast thou prepared me:
This human body was indwelt by all the fullness of God's nature.
Colossians 1:19 Young's Literal Translation (YLT)
because in him it did please all the fulness to tabernacle,
Colossians 2:8-9 Beware lest any man spoil you through philosophy and vain deceit, after the tradition of men, after the rudiments of the world, and not after Christ. For in him dwelleth all the fulness of the Godhead bodily.
