"The purpose of the cross is not to arouse pity in us, neither is it merely some general display of the love of God. Not at all! It is finally understood only in terms of the law. What was happening upon the cross was that out Lord and Saviour Jesus Christ, the Son of God, was enduring in His own holy body the penalty prescribed by the holy law of God for the sin of man. The law condemns sin, and the condemnation that it pronounces is death. 'The wages of sin is death.' The law pronounces that death must pass upon all who have sinned against God and broken His holy law. Christ says, 'Think not that I am come to destroy the law, or the prophets; I am not come to destroy, but to fulfil.' One of the ways in which the law has to be fulfilled is that its punishment of sin must be carried out. This punishment is death, and that was why He died. The law must be fulfilled. God cannot put it on one side in any respect, and the punishment cannot be put on one side. God in forgiving us -- let us say so clearly -- does not do so by deciding not to exact the punishment that He has decreed. That would imply a contradiction of His holy nature. Whatever God says must be brought to pass. He does not go back upon Himself and upon what He says. He has said that sin has to be punished by death, and you and I can be forgiven only because the punishment has been thus exacted. In respect of its punishment of sin God's law has been fulfilled absolutely, because He has punished sin in the holy, spotless, blameless body of His own Son there upon the cross on Calvary's hill. Christ is fulfilling the law on the cross..."
~Martin Lloyd Jones, Studies in the Sermon on the Mount, Chapter 18: "Christ Fulfilling the Law and the Prophets".
"But now the righteousness of God has been manifested apart from the law, although the Law and the Prophets bear witness to it— the righteousness of God through faith in Jesus Christ for all who believe. For there is no distinction: for all have sinned and fall short of the glory of God, and are justified by his grace as a gift, through the redemption that is in Christ Jesus, whom God put forward as a propitiation by his blood, to be received by faith. This was to show God's righteousness, because in his divine forbearance he had passed over former sins. It was to show his righteousness at the present time, so that he might be just and the justifier of the one who has faith in Jesus."
"For the wages of sin is death, but the free gift of God is eternal life in Christ Jesus our Lord."