The Heidelberg Catechism, This Lord's Day week 13

Q33: Why is He called God's "only begotten Son," since we also are the children of God?

A33: Because Christ alone is the eternal, natural Son of God,[1] but we are the children of God by adoption, through grace, for His sake.[2]
1. John 1:14, 182. Rom. 8:15-17; Eph. 1:5-6; I John 3:1

Q34: Why do you call Him "our Lord"?

A34: Because not with silver or gold, but with His precious blood, He has redeemed and purchased us, body and soul, from sin and from all the power of the devil, to be His own.[1]
1. I Peter 1:18-19; 2:9; I Cor. 6:20; 7:23; Acts 2:36; Titus 2:14; Col. 1:14