Q16: Why must He be truly human and truly righteous?
A16: God's justice demands that human nature, which has sinned, must pay for its sin; but a sinner could never pay for others.
Q17: Why must He also be truly God?
A17: So that, by the power of His divinity, He might bear the weight of God's anger in His humanity and earn for us and restore to us righteousness and life.
Q18: And who is this Mediator—true God and at the same time truly human and truly righteous?
A18: Our Lord Jesus Christ, who was given us to set us completely free and to make us right with God.
Q19: How do you come to know this?
A19: The holy gospel tells me. God Himself began to reveal the gospel already in Paradise; later, He proclaimed it by the holy patriarchs and prophets, and portrayed it by the sacrifices and other ceremonies of the law; finally He fulfilled it through His own dear Son.