Every religion asks how people can be made right with God. Most answers are about trying harder. The Bible's answer is surprising: we can't — but God can.
"For all have sinned and fall short of the glory of God, and are justified by his grace as a gift, through the redemption that is in Christ Jesus" (Romans 3:23–24, ESV). "Justified" means declared right with God — not because we are good, but because Jesus is, and he stood in our place.
How do we receive it? By faith — trusting Jesus rather than ourselves. "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." (Ephesians 2:8–9, ESV)
Faith isn't a feeling we work up; it's leaning our whole weight on Jesus. And the Bible says it brings complete security: "There is therefore now no condemnation for those who are in Christ Jesus." (Romans 8:1, ESV)
Go deeper: R. C. Sproul, How Can I Be Right with God? (free ebook, Ligonier) · C. H. Spurgeon, All of Grace (free, CCEL).