look at John 17 “that they may all be one, as you, Father, are in me and I in you”
or at Matthew 1 "All this took place to fulfill what the Lord had said through the prophet: “The virgin will be with child and will give birth to a son, and they will call him Immanuel”—which means, “God with us.” "
additionally, You can look at the Creed, which says in part
“We believe in one Lord, Jesus Christ,
the only Son of God,
eternally begotten of the Father,
God from God, Light from Light,
true God from true God,
begotten, not made,
one in being with the Father.”
emphasis mine
Begotten, as opposed to made, has the connotations of being of the same kind. As humans, we beget children, we make robots.
God from God-again emphasizing that the Father and the Son are of the same being
One in Being-more accurately, and this change is being made, consubstantial with-of the same substance.
The Father and the Son (and the Holy Spirit) are of the same substance, there is only One God