Can a believer in Jesus backslide out of salvation?
The quick answer is, no, and that is simply because the Father is not a failure and is faithful to finish the Work that He started...
He knocks at the door…
Never trust in head knowledge or your mind to try to understand the Mind of God. You end up having knowledge from the world in your heart when you do this, instead of having the Word of God in your heart —which gives access to the thoughts of God when you believe in His Word. Jesus is the Word of God and He stands at the door knocks… He stands at the door of your heart.