"To wit, that God was in Christ, reconciling the world unto himself, not imputing their trespasses unto them; and hath committed unto us the word of reconciliation. Now then we are ambassadors for Christ, as though God did beseech you by us: we pray you in Christ's stead, be ye reconciled to God. For he hath made him to be sin for us, who knew no sin; that we might be made the righteousness of God in him."
Like all those who have come before throughout the history of the world, we were born as sinners. No one starts out good and then turns bad. We start out with a sinful nature. David wrote, “The wicked are estranged from the womb: they go astray as soon as they be born, speaking lies” (Psalm 58:3). That sinful nature prevents us from being able to do anything to earn or deserve the salvation we need. And that is why Jesus came as the sacrifice for sin that allows Him to be the Savior of those who believe.
Oswald Chambers wrote, “God made His own Son to be sin that He might make the sinner a saint. All through the Bible it is revealed that our Lord bore the sin of the world by identification, not by sympathy. He deliberately took upon His own shoulders, and bore in His own Person, the whole massed sin of the human race and by so doing He put the whole human race on the basis of Redemption.”
Only perfect righteousness is enough to allow us to stand in God's presence, but we could never attain it on our own. In grace, God offers the perfect righteousness of Jesus to be applied to our account. This righteousness is only available to us because Jesus took all of our sins and applied them to His account, though He was sinless, and suffered the penalty for those sins so that we do not have to experience Hell.
By accepting the gift of salvation Jesus offers by grace alone, we become righteous and are fully accepted by God.