The devil's primary goal is to keep us away from Christ but if we do give our lives to Him, the devil will still try to fill us with doubt and fear. And one of his oldest tricks is to get us to doubt our salvation.
The Bible is clear: Once we truly give our lives to Jesus Christ and trust Him alone for our salvation, God cleanses us from all our sins and makes us members of His family forever. The Bible says, "The blood of Jesus, his Son, purifies us from all sin" (1 John 1:7). If we lost our salvation every time we sinned, then we'd lose our salvation every day because we sin every day. We may not even be aware of our sins, but an impure thought or an unkind word is sin in God's eyes.
The key is to remember this: Your salvation does not depend on you, but on Christ. If it depended on you, you could never be saved, because you are never good enough. But your salvation depends solely on Christ and what He did for you on the cross. Why not pause right now and thank Him for being willing to die for you? God loves you that much!
Sin is still serious, however; when we sin, we hurt our fellowship with God. But we are still His children if we know Christ, and nothing "will be able to separate us from the love of God that is in Christ Jesus our Lord" (Romans 8:39).