“Once saved always saved” is the main problem, which gives people a license to sin. We must actually abide in Christ to be “in Christ,” the New Testament clearly says:

Who-Goes-To-Heaven Scriptures — Narrow is the Way | Who are the Children of God? — “There is therefore now *no condemnation* to those who are IN CHRIST Jesus, who don’t WALK according to the flesh, but ACCORDING TO THE SPIRIT”