The Bible says that every single person has sinned against God, including those who do their best to be good people. Romans 3:22-23 says, “For there is no difference; for all have sinned and fall short of the glory of God.”
Sin separates us from God. He is perfect, holy, and just. Sin is an affront to all that God is and does. He cannot allow sin into His presence. No matter how many good deeds we do, we can't erase the sins that we've committed against God.
Yet at the same time, God loves us. So if God could have a problem, this would present Him with one: How can He love and forgive the sinner and at the same time punish sin?
The answer? By sending Jesus to die for our sins. God’s Lamb took the sin of the world and suffered as
an innocent substitute—the just for the unjust—that He might bring us to God. God is just because sin is
punished. He’s the justifier because we have a substitute. Mercy and justice meet together in the cross.