As Christians, we see the work of Christ on the cross as the only solution to the problem of sin. We believe that Christ had to die in order for any sinners to be saved. If God is completely sovereign over all things, however, why is atonement necessary? Why could God not simply decide that He would forgive somebody’s sins if He wanted?
The answer to the question lies not in any limitation of God’s sovereign power but rather in the essence of His character. The Bible teaches that God is sovereign (Ps. 135:6, Ps. 115:3, Is. 46:10). Nothing outside of God limits His power. He is, however, self-limited. God cannot act contrary to His own nature or He would cease to be the God revealed in His Word. The God of the Bible is perfect in all of His attributes. He is perfectly holy, just, and true. His power is therefore always consistent with those attributes, always consistent with who He is, and there is no shadow of turning with Him (Jas. 1:17).
This idea of divine self-limitation is not speculative theology, it is revealed in the Bible in several places. It is perhaps most clear in the sixth chapter of Hebrews where the writer explains that God could not swear by any name greater than His own and that He cannot lie (Heb. 6:13-18). God does what He wills but always does it in a way that is true to who He is. The Bible reveals that not only is God sovereign, but He is also holy, righteous, and just (Is. 6:3, Is. 5:16, Job 37:23).
The perfection of God makes the atonement necessary because God cannot be righteous if He allows sin to go unpunished. Unlike Islam, which teaches that Allah can simply use his sovereign power to disregard the sinfulness of those he chooses and allow them into paradise, the Christian God does not undermine His own law (thus denying His holy character) in order to do so. God is so holy that any sin is a form of cosmic rebellion and if God did not punish such treason, His righteousness and justice are compromised.
Suppose that a man was a guilty of a brutal crime such as rape or murder and the evidence of his guilt was unquestioned. Now, suppose that the man is brought before a judge and despite the evidence, the judge decides to let him go. Not only does the judge let him go, but gives him great honors and comforts. We all agree this would be a great injustice and an unrighteous judgment. In the case of salvation, the offensiveness of the crime is far worse and the mercy of the court is a far more outrageous pardon.
This brings us to one of the most fundamental theological problems for fallen humankind. How is it possible for a holy, righteous God to save sinners without being unjust? How can God fulfill the promises He has made to rebellious sinners without compromising His own perfect character?
The answer is the Gospel. The apostle Paul explains in the letter to the Romans:
“…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.” (Romans 3:23-26)
It was not enough for sinners simply to be pardoned; they must be justified in a way that is consistent with the righteousness of God. Since none are righteous and all have sinned the solution had to come from God (Rom. 3:10, Eph. 2:4-5), while the only appropriate representative to provide atonement had to be human (Rom. 5:15, 8:3-4). Therefore, God was pleased to offer salvation through faith in the God-man Jesus Christ. Our sins, however, are not simply ignored.
Notice what Paul says about this atoning sacrifice, “This was to show God's righteousness, because in his divine forbearance he had passed over former sins.” In order for the righteousness of God to remain uncompromised, He had to judge sin. The suffering of Christ was a demonstration of God’s holy wrath against sin so that no valid charge of injustice or unrighteousness can be made. This is why Paul says Christ is a “propitiation”, which means that He satisfies the wrath of God. All sin is therefore justly punished; the question is if Jesus pays for our sin or if we will have to pay the penalty ourselves.
Paul goes on to say, “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.” Because of the atoning work of Jesus Christ, God is both just and the justifier of sinners. The cross is where God’s mercy and His justice come together.
The atonement is necessary in order to for a holy God to save sinners without compromising His justice. He does not act contrary to His own nature. Salvation is the result of God’s sovereignty, but not as an expression of brute power. Instead, God’s sovereign work in the salvation of sinners is a demonstration of His love and mercy.
The perfect balance of power and love that is expressed in the cross of Jesus Christ is not only a theological necessity but is a great comfort to believers. Since God’s righteousness, grace, and power are all perfectly displayed in Christ, we can look to the cross as assurance that God will keep His promises (Rom. 8:32). Christians are not hoping on the whim of a changing God for their salvation. We trust in the promises of a perfect, righteous, holy, and loving God who has already demonstrated His commitment to those whom He loves.