I am copying and linking to Lord’s Day 6 of the Heidelberg Catechism (1563).

This text comes from the Heidelblog.net publication of the Catechism (accessed 5 March 2023).
Q16. Why must he be a true and righteous man?
A. Because the justice of God requires1 that the same human nature which has sinned should make satisfaction for sin, but one who is himself a sinner, cannot satisfy for others.2
Q17. Why must he also be true God?
A. That by the power of His Godhead He might bear in His manhood the burden of God’s wrath,1 and so obtain for2 and restore to us righteousness and life.3
1Isaiah 53:8. Acts 2:24. 2John 3:16. Acts 20:28. 3I John 1:2.
Q18. But who now is that Mediator, who in one person is true God and also a true and righteous man?
A. Our Lord Jesus Christ,1 who is freely given unto us for complete redemption and righteousness.2
1 Matt 1:23. 1 Tim 3:16. Luke 2:11. 21 Cor 1:30. * Acts 4:12.
Q19. From where do you know this?
A. From the Holy Gospel, which God Himself revealed first in Paradise;1 afterwards proclaimed by the holy Patriarchs2 and Prophets, and foreshadowed by the sacrifices and other ceremonies of the law;3 and finally fulfilled by His well-beloved Son.
1Gen 3:15. 2Gen 22:18. Gen 49:10,11. Rom 1:2. Heb 1:1. Acts 3:22-24. Acts 10:43. 3John 5:46. Heb 10:7. 4Rom 10:4. Gal 4:4,5. * Heb 10:1.
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Thank you