Why is Christ called the “only begotten Son” of God, since we are also the children of God?
Because Christ alone is the eternal and natural Son of God; but we are children adopted of God, by grace, for his sake.
John 1:1–3 1 In the beginning was the Word, and the Word was with God, and the Word was God. 2 He was in the beginning with God. 3 All things were made through him, and without him was not any thing made that was made.
John 1:14 And the Word became flesh and dwelt among us, and we have seen his glory, glory as of the only Son from the Father, full of grace and truth.