Please note "who" is speaking in
Hebrews 1. God is saying:
"But unto the Son he saith,
Thy throne, O God, is for ever and ever: a sceptre of righteousness is the sceptre of thy kingdom."
When God speaks, he speaks to the source. In
Genesis 1, He speaks to the elements, "Let the earth bring forth grass, the herb yielding seed, and the fruit tree yielding fruit after his kind, whose seed is in itself..."
The ground is the plant source.
When He speaks to and of Himself, He is speaking to the source. That is why He can emphatically say unto the "son", "They throne, O God..."
He is God, the father and the son.
"Who is the image of the invisible God, the firstborn of every creature."
Colossians 1:15
Jesus Christ is presented here as the image of God, the invisible. "Image" in Greek,
Eikon always assumes a prototype (the original form from which it is drawn), not merely a thing it resembles (e.g., the reflection of the sun in the water is an
eikon). Paul was telling the Colossians here that Jesus Christ has a "prototype", God the Father who is invisible. - Spiros Zodhiates
"But made himself of no reputation, and took upon him the form of a servant, and made in the likeness of men."
Philippians 2:7
The phrase in verse seven, "took upon him the form of a servant," should be understood as "having taken..." which denotes that He became as a servant in man's likeness at His incarnation, and that he did not possess that form before that time. His purpose in coming as a man in order to die for the sins of mankind. The key idea to consider is that Christ was and is who He claimed to be - God. - Spiros Zodhiates