Question: What kind of Surety and Mediator should we look for then?
Answer: One who is at the same time truly human and righteous and yet more powerful than any creature, that is, true, eternal God. This person is Jesus Christ — crucified and raised again on our behalf, the only way to eternal life, whom God Himself from the beginning revealed from heaven to the poor, lost human race. For the merciful Father did not wait until humanity came to Him and asked for grace. Rather, He approached humanity, who had fled from Him, and out of His great mercy gave humanity His promise that He would restore it. He first gave this promise to Adam in Genesis 3:15: “I will put emnity,” says the Lord to the serpent, “between you and the woman, between your seed and her seed; He shall crush your head, and you shall sting his heel.” Later He gave the promise even more clearly to Abraham and his descendants: “By Myself I have sworn, says the Lord . . . In your seed all the nations of the earth shall be blessed.” (Genesis 22:16, 18) Finally, the promise was given also to David, as in Psalm 89:
3 “I have made a covenant with My chosen;
I have sworn to David My servant,
4 I will establish your seed forever
And build up your throne to all generations.” Psalm 89:3, 4
28 “My loving-kindness I will keep for him forever,
And My covenant shall be confirmed to him.
29 “So I will establish his descendants forever
And his throne as the days of heaven. Psalm 89:28, 29
33 “But I will not break off My loving-kindness from him,
Nor deal falsely in My faithfulness.
34 “My covenant I will not violate,
Nor will I alter the utterance of My lips.
35 “Once I have sworn by My holiness;
I will not lie to David.
36 “His descendants shall endure forever
And his throne as the sun before Me.
37 “It shall be established forever like the moon,
And the witness in the sky is faithful.” Psalm 89:33-37
Hence Christ also, because of the promise given to David, is called the son of David.
This Savior, promised by God and then sent into the world, is Christ Jesus — truly human and righteous and at the same time more powerful than any creature, that ids, true, eternal God, who gave Himself as a sacrifice on the cross to pay for all our sins. The Father Himself bears witness of Him from heaven: “This is My beloved Son in whom I am well pleased. Hear Him!” (Matthew 17:5) And Christ confirms this testimony of the Father when He says, “I am the way, the truth, and the life.” (John 14:6)
Caspar Olevianus, A Firm Foundation, p. 4