Because the justice of God requires that the same human nature
which has sinned should make satisfaction for sin; but one who is himself a
sinner cannot satisfy for others.
17. Why must He also be true God?
That by the power of His Godhead He might bear in His manhood the
burden of God's wrath, and so obtain for and restore to us righteousness and
life.
18. But who now is that Mediator, who in one person is true God
and also a true and righteous man?
Our Lord Jesus Christ, who is freely given unto us for complete
redemption and righteousness.
19. From where do you know this?
From the Holy Gospel, which God Himself first revealed in
Paradise, afterwards proclaimed by the holy patriarchs and prophets, and
foreshadowed by the sacrifices and other ceremonies of the law, and finally
fulfilled by His well-beloved Son.