Because Jesus took sin into Himself on the cross so God could pour out His wrath for sin:
God is not putting sins into anyone's account.
God is not counting anyone's sins.
God is not charging anyone with sin.
God is not crediting anyone with sin.
God doing this makes relationship with Himself 100% freely available to all who choose to trust Jesus.
Jesus took everyone's sins into His account. They were counted, charged, and credited against Him. The Son of God paid all of the judgment & punishment required for all sins on the cross. When Jesus said "It is finished" that was a term that also meant "paid in full." Because of Jesus God no longer looks at anyone with regard to sin. God does not relate to anyone based on sin!
Sin is not being charged to the world. The sins of the world are taken away. After Jesus rose to life we now live in a pure relational reality with no spiritual barriers standing between us and God. The words believe and faith both mean trust. Choosing to trust the person of Jesus is the only requirement of salvation.
I can either choose to trust a person to engage in a relationship with that person or I can choose not to trust that person and thus have no relationship with them. Salvation is a pure relational reality that is offered with no spiritual barriers. No barriers of sin, work, deed, or law ever exist for anyone because of the cross! Trust Jesus and live loved!
"God the Father was in Christ on the cross making relationship with Himself available to the world by no longer counting people's sins against them. God has given us this message of relationship to tell others. We beg you on behalf of Christ to come to God." (2 Corinthians 5:19-20)