Sin is both doing what God forbids and failing to do what He commands. Every person has sinned and falls short of God's holiness, and that sin separates us from Him.
Romans 3:23 (ESV): "For all have sinned and fall short of the glory of God."

The result of sin is death — spiritual and eternal separation from God.
Romans 6:23 (ESV): "For the wages of sin is death, but the free gift of God is eternal life in Christ Jesus our Lord."

God sent His Son Jesus to take our place, dying on the cross and rising again so we could be reconciled to God by grace through faith.
Ephesians 2:8–9 (ESV): "For by grace you have been saved through faith. And this is not your own doing; it is the gift of God, not a result of works, so that no one may boast."

Once we surrender to Jesus, we are fully justified by His grace and made new. The Holy Spirit comes to dwell within us, empowering us to live transformed lives.
2 Corinthians 5:17 (ESV): "Therefore, if anyone is in Christ, he is a new creation. The old has passed away; behold, the new has come."