If you only understand one thing from the Bible, this should be it. We stand guilty before God – when we measure ourselves against his law we all fall flat. The good news then is that God justifies us (counts us sinless before him) by faith in the blood of Jesus Christ who died for our sins. This is the only way to be saved – because it does not matter how good we think we have been, we are still unrighteous and condemned to hell if measured by our deeds.
But now the righteousness of God has been manifested apart from the law, although the Law and the Prophets bear witness to it— the righteousness of God through faith in Jesus Christ for all who believe. For there is no distinction: 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, whom God put forward as a propitiation by his blood, to be received by faith.