Who is the invisible God that the Son is the image of?
The invisible God is the triune God: God the Father, God the Son, and God the Spirit. They are Spirit and were invisible. Out of that invisible triune God, the Son stepped forth and became visible, tangible, and touchable, especially in the New Testament through Bethlehem.
Les explains from Colossians 1:15 that the pronoun “who” refers back to the Son in verse 13, the One in whom we have redemption. Verse 15 calls the Son the image, the visible, tangible evidence, of the invisible God. The question then is who is that invisible God? The context answers: the triune God—God the Father, God the Son, and God the Spirit. They are Spirit, and they were invisible. Yet out of that invisible triune God, the Son stepped forth. He became visible in the Old Testament economy temporarily and then would disappear, but in the New Testament account He became visible, tangible, and touchable. He lived in the flesh by virtue of Bethlehem. It is the same God now manifested in the flesh by the Son.
Who is the image of the invisible God, the firstborn of every creature: