Westminster Q71: How is justification an act of God's free grace?

(Rom 5:8-10, 19) But God demonstrates His own love toward us, in that while we were yet sinners, Christ died for us. Much more then, having now been justified by His blood, we shall be saved from the wrath of God through Him. For if while we were enemies we were reconciled to God through the death of His Son, much more, having been reconciled, we shall be saved by His life. . . . For as through the one man's disobedience the many were made sinners, even so through the obedience of the One the many will be made righteous.
(2Ti 2:5-6) Also if anyone competes as an athlete, he does not win the prize unless he competes according to the rules. The hard-working farmer ought to be the first to receive his share of the crops.

(Heb 7:22) so much the more also Jesus has become the guarantee of a better covenant.

(Heb 10:10) By this will we have been sanctified through the offering of the body of Jesus Christ once for all.

(Mat 20:28) just as the Son of Man did not come to be served, but to serve, and to give His life a ransom for many."

(Dan 9:24, 26) "Seventy weeks have been decreed for your people and your holy city, to finish the transgression, to make an end of sin, to make atonement for iniquity, to bring in everlasting righteousness, to seal up vision and prophecy and to anoint the most holy place. . . "Then after the sixty-two weeks the Messiah will be cut off and have nothing, and the people of the prince who is to come will destroy the city and the sanctuary. And its end will come with a flood; even to the end there will be war; desolations are determined.

(Isa 53:4-6, 10-12) Surely our griefs He Himself bore, And our sorrows He carried; Yet we ourselves esteemed Him stricken, Smitten of God, and afflicted. But He was pierced through for our transgressions, He was crushed for our iniquities; The chastening for our well-being fell upon Him, And by His scourging we are healed. All of us like sheep have gone astray, Each of us has turned to his own way; But the LORD has caused the iniquity of us all To fall on Him. . . But the LORD was pleased To crush Him, putting Him to grief; If He would render Himself as a guilt offering, He will see His offspring, He will prolong His days, And the good pleasure of the LORD will prosper in His hand. As a result of the anguish of His soul, He will see it and be satisfied; By His knowledge the Righteous One, My Servant, will justify the many, As He will bear their iniquities. Therefore, I will allot Him a portion with the great, And He will divide the booty with the strong; Because He poured out Himself to death, And was numbered with the transgressors; Yet He Himself bore the sin of many, And interceded for the transgressors.

(Rom 8:32) He who did not spare His own Son, but delivered Him over for us all, how will He not also with Him freely give us all things?

(1Pe 1:18-19) knowing that you were not redeemed with perishable things like silver or gold from your futile way of life inherited from your forefathers, but with precious blood, as of a lamb unblemished and spotless, the blood of Christ.
(2Co 5:21) He made Him who knew no sin to be sin on our behalf, so that we might become the righteousness of God in Him.
(Rom 3:24-25) being justified as a gift by His grace through the redemption which is in Christ Jesus; whom God displayed publicly as a propitiation in His blood through faith. This was to demonstrate His righteousness, because in the forbearance of God He passed over the sins previously committed;
(Eph 2:8) For by grace you have been saved through faith; and that not of yourselves, it is the gift of God;
(Eph 1:7) In Him we have redemption through His blood, the forgiveness of our trespasses, according to the riches of His grace