God publicly displayed him at his death as the mercy seat accessible through faith. This was to demonstrate his righteousness, because God in his forbearance had passed over the sins previously committed. (Romans 3:25 NET)
"Therefore, having overlooked the times of ignorance, God now commands all people everywhere to repent, because he has set a day when he is going to judge the world in righteousness by the man he has appointed. He has provided proof of this to everyone by raising him from the dead." (Acts 17:30-31CSB)
He is the propitiation for our sins, and not for ours only but also for the sins of the whole world. (1 John 2:2 ESV)
God does not condone sin. But God can overlook all sin legally and allow sinners to live without being unjust because He had sent His Son Jesus to die for the sins of the world, past, present and future. Thus when Adam sinned, the world was not destroyed straightaway. God can now be justified when He allow us to live while we are yet sinners, giving us an opportunity to be saved. Mercy and justice are reconciled in Christ Jesus.
Since they thought it foolish to acknowledge God, he abandoned them to their foolish thinking and let them do things that should never be done. Their lives became full of every kind of wickedness, sin, greed, hate, envy, murder, quarreling, deception, malicious behavior, and gossip. They are backstabbers, haters of God, insolent, proud, and boastful. They invent new ways of sinning, and they disobey their parents. They refuse to understand, break their promises, are heartless, and have no mercy. They know God's justice requires that those who do these things deserve to die, yet they do them anyway. Worse yet, they encourage others to do them, too. You may think you can condemn such people, but you are just as bad, and you have no excuse! When you say they are wicked and should be punished, you are condemning yourself, for you who judge others do these very same things. And we know that God, in his justice, will punish anyone who does such things. Since you judge others for doing these things, why do you think you can avoid God's judgment when you do the same things? Don't you see how wonderfully kind, tolerant, and patient God is with you? Does this mean nothing to you? Can't you see that his kindness is intended to turn you from your sin? (Romans 1:28-2:4 NLT)
Your eyes are too pure to look on evil; you cannot tolerate wrongdoing. Why then do you tolerate the treacherous? Why are you silent while the wicked swallow up those more righteous than themselves? (Habakkuk 1:13 NIV)
Many people are confused by God's mercy. When they see the wicked who sinned terribly live without suffering any consequences, they demand that God punishes them. But they overlooked that they themselves are also sinners who commit small sins. They forgot that God is just and punishes all sin, big and small. Because their own sins are small, they did not see them as sin and thought they are righteous.
For everyone has sinned; we all fall short of God's glorious standard. Yet God, in his grace, freely makes us right in his sight. He did this through Christ Jesus when he freed us from the penalty for our sins. For God presented Jesus as the sacrifice for sin. People are made right with God when they believe that Jesus sacrificed his life, shedding his blood. This sacrifice shows that God was being fair when he held back and did not punish those who sinned in times past, for he was looking ahead and including them in what he would do in this present time. God did this to demonstrate his righteousness, for he himself is fair and just, and he makes sinners right in his sight when they believe in Jesus. (Romans 3:23-26 NLT)