How did the Son come to live in the flesh?

The Son came to live in the flesh by virtue of Bethlehem—His birth into humanity. Out of the invisible triune God, the Son stepped forth and became visible, tangible, and touchable in the New Testament account, the same God now manifested in the flesh as the Son.

Les explains that the Son is the image, the visible and tangible evidence, of the invisible God. 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 stepped the Son. In the Old Testament economy He became visible 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. So it is the same God now manifested in the flesh by the Son.

Colossians 1:15

Who is the image of the invisible God, the firstborn of every creature:

How did the Son of the invisible God become visible to people?

The Son, who is the image of the invisible God, became visible tangibly. In the Old Testament economy He appeared temporarily then disappeared. In the New Testament He became visible, tangible, and touchable, living in the flesh by virtue of Bethlehem—God manifested in the flesh by the Son.