For God so loved the world, that He gave His only begotten Son, that whoever believes in Him shall not perish, but have eternal life. For God did not send the Son into the world to judge the world, but that the world might be saved through Him. He who believes in Him is not judged; he who does not believe has been judged already, because he has not believed in the name of the only begotten Son of God.
Your acceptance with God is based on what He has done, not on what you do!
Jesus had to tell Nicodemus not to be amazed at this truth. Nicodemus was an ultra-righteous religious leader. He thought that you had to complete a list of good deeds to be acceptable to God. And even if you did the things, there was always that niggling doubt that maybe you had not done enough.
But what Jesus tells him is that no one can become acceptable to God by doing good deeds, because even the smallest bit of sin separates us from God. The only way we could be saved was for Jesus to take the penalty for our sins. That is what He did when He died on the cross for us — He took our place! Today Jesus offers you forgiveness and acceptance as a gift, based on what He has done, not on your religiosity.