Heidelberg Catechism – Lord’s Day 13
Q. Why is he called God’s only begotten Son, since we also are God’s children?
A. Because Christ alone is God’s own eternal Son, whereas we are accepted for his sake as children of God by grace.
Q. Why do you call him our Lord?
A. Because, not with gold or silver but at the cost of his blood, he has redeemed us body and soul from sin and all the dominion of the devil, and has bought us for his very own.