Holy Bible: 1 JOHN 2:3

"And hereby we do know that we know him, if we keep his commandments."

We know God, if we keep his commandments. If someone says "I know God" or "I believe in God," but they don't obey his commandments, they are liars. If they believed in God, they'd believe in what God said about disobeying his commandments: eternal death.

Now, we all have sinned, but if we believe in Jesus Christ, our sins are cleansed and wiped away. And we are made new, purified, and we become set free from the bondage of sin. When we believe, we no longer sin.