The Heidelberg Catechism Part II: Deliverance Lord’s Day 6
Question 16: Why must the mediator be a true and righteous human?
Answer 16: God’s justice demands that human nature, which has sinned, must pay for sin;  but a sinful human could never pay for others. 
 Romans 5:12 NKJV Therefore, just as through one man sin entered the world, and death through sin, and thus death spread to all men, because all sinned--
Romans 5:15 NKJV But the free gift is not like the offense. For if by the one man's offense many died, much more the grace of God and the gift by the grace of the one Man, Jesus Christ, abounded to many.
1 Corinthians 15:21 NKJV For since by man came death, by Man also came the resurrection of the dead.
Hebrews 2:14-16 NKJV Inasmuch then as the children have partaken of flesh and blood, He Himself likewise shared in the same, that through death He might destroy him who had the power of death, that is, the devil, (15) and release those who through fear of death were all their lifetime subject to bondage. (16) For indeed He does not give aid to angels, but He does give aid to the seed of Abraham.
 Hebrews 7:26-27 NKJV For such a High Priest was fitting for us, who is holy, harmless, undefiled, separate from sinners, and has become higher than the heavens; (27) who does not need daily, as those high priests, to offer up sacrifices, first for His own sins and then for the people's, for this He did once for all when He offered up Himself.
1 Peter 3:18 NKJV For Christ also suffered once for sins, the just for the unjust, that He might bring us to God, being put to death in the flesh but made alive by the Spirit,
Q17: Why must the mediator also be true God?
A17: So that the mediator, by the power of his divinity, might bear the weight of God’s wrath in his humanity and earn for us and restore to us righteousness and life. 
 Isaiah 53:1-12 NKJV Who has believed our report? And to whom has the arm of the LORD been revealed? (2) For He shall grow up before Him as a tender plant, And as a root out of dry ground. He has no form or comeliness; And when we see Him, There is no beauty that we should desire Him. (3) He is despised and rejected by men, A Man of sorrows and acquainted with grief. And we hid, as it were, our faces from Him; He was despised, and we did not esteem Him. (4) Surely He has borne our griefs And carried our sorrows; Yet we esteemed Him stricken, Smitten by God, and afflicted. (5) But He was wounded for our transgressions, He was bruised for our iniquities; The chastisement for our peace was upon Him, And by His stripes we are healed. (6) All we like sheep have gone astray; We have turned, every one, to his own way; And the LORD has laid on Him the iniquity of us all. (7) He was oppressed and He was afflicted, Yet He opened not His mouth; He was led as a lamb to the slaughter, And as a sheep before its shearers is silent, So He opened not His mouth. (8) He was taken from prison and from judgment, And who will declare His generation? For He was cut off from the land of the living; For the transgressions of My people He was stricken. (9) And they made His grave with the wicked—But with the rich at His death, Because He had done no violence, Nor was any deceit in His mouth. (10) Yet it pleased the LORD to bruise Him; He has put Him to grief. When You make His soul an offering for sin, He shall see His seed, He shall prolong His days, And the pleasure of the LORD shall prosper in His hand. (11) He shall see the labor of His soul, and be satisfied. By His knowledge My righteous Servant shall justify many, For He shall bear their iniquities. (12) Therefore I will divide Him a portion with the great, And He shall divide the spoil with the strong, Because He poured out His soul unto death, And He was numbered with the transgressors, And He bore the sin of many, And made intercession for the transgressors.
John 3:16 NKJV For God so loved the world that He gave His only begotten Son, that whoever believes in Him should not perish but have everlasting life.
2 Corinthians 5:21 NKJV For He made Him who knew no sin to be sin for us, that we might become the righteousness of God in Him.
Q18: Then who is this mediator – true God and at the same time a true and righteous human?
A18: Our Lord Jesus Christ,  who was given to us to completely deliver us and make us right with God. 
 Matthew 1:21-23 NKJV And she will bring forth a Son, and you shall call His name JESUS, for He will save His people from their sins." (22) So all this was done that it might be fulfilled which was spoken by the Lord through the prophet, saying: (23) "Behold, the virgin shall be with child, and bear a Son, and they shall call His name Immanuel," which is translated, "God with us."
Luke 2:11 NKJV For there is born to you this day in the city of David a Savior, who is Christ the Lord.
1 Timothy 2:5 NKJV For there is one God and one Mediator between God and men, the Man Christ Jesus,
 1 Corinthians 1:30 NKJV But of Him you are in Christ Jesus, who became for us wisdom from God – and righteousness and sanctification and redemption –
Q19: How do you come to know this?
A19: The holy gospel tells me. God began to reveal the gospel already in Paradise;  later God proclaimed it by the holy patriarchs  and prophets  and foreshadowed it by the sacrifices and other ceremonies of the law;  and finally God fulfilled it through his own beloved Son. 
 Genesis 3:15 NKJV And I will put enmity Between you and the woman, And between your seed and her Seed; He shall bruise your head, And you shall bruise His heel."
 Genesis 22:18 NKJV In your seed all the nations of the earth shall be blessed, because you have obeyed My voice."
Genesis 49:10 NKJV The scepter shall not depart from Judah, Nor a lawgiver from between his feet, Until Shiloh comes; And to Him shall be the obedience of the people.
 Isaiah 53 (see above)
Jeremiah 23:5-6 NKJV "Behold, the days are coming," says the LORD, "That I will raise to David a Branch of righteousness; A King shall reign and prosper, And execute judgment and righteousness in the earth. (6) In His days Judah will be saved, And Israel will dwell safely; Now this is His name by which He will be called: The LORD our Righteousness.
Micah 7:18-20 NKJV Who is a God like You, Pardoning iniquity And passing over the transgression of the remnant of His heritage? He does not retain His anger forever, Because He delights in mercy. (19) He will again have compassion on us, And will subdue our iniquities. You will cast all our sins Into the depths of the sea. (20) You will give truth to Jacob And mercy to Abraham, Which You have sworn to our fathers From days of old.
Acts 10:43 NKJV To Him all the prophets witness that, through His name, whoever believes in Him will receive remission of sins."
Hebrews 1:1-2 NKJV God, who at various times and in various ways spoke in time past to the fathers by the prophets, (2) has in these last days spoken to us by His Son, whom He has appointed heir of all things, through whom also He made the worlds;
 Leviticus, chapters 1-7
John 5:46 NKJV For if you believed Moses, you would believe Me; for he wrote about Me.
Hebrews 10:1-10 NKJV For the law, having a shadow of the good things to come, and not the very image of the things, can never with these same sacrifices, which they offer continually year by year, make those who approach perfect. (2) For then would they not have ceased to be offered? For the worshipers, once purified, would have had no more consciousness of sins. (3) But in those sacrifices there is a reminder of sins every year. (4) For it is not possible that the blood of bulls and goats could take away sins. (5) Therefore, when He came into the world, He said: "Sacrifice and offering you did not desire, but a body you have prepared for Me. (6) In burnt offerings and sacrifices for sin You had no pleasure. (7) Then I said, 'Behold, I have come — in the volume of the book it is written of Me — to do Your will, O God.' " (8) Previously saying, "Sacrifice and offering, burnt offerings, and offerings for sin You did not desire, nor had pleasure in them" (which are offered according to the law), (9) then He said, "Behold, I have come to do Your will, O God." He takes away the first that He may establish the second. (10) By that will we have been sanctified through the offering of the body of Jesus Christ once for all.
 Romans 10:4 NKJV For Christ is the end of the law for righteousness to everyone who believes.
Galatians 4:4-5 NKJV But when the fullness of the time had come, God sent forth His Son, born of a woman, born under the law, (5) to redeem those who were under the law, that we might receive the adoption as sons.
Colossians 2:16-17 NKJV So let no one judge you in food or in drink, or regarding a festival or a new moon or sabbaths, (17) which are a shadow of things to come, but the substance is of Christ.