Many sincere religious people believe that once a sinner has been redeemed by Christ, it is impossible for him to so sin as to fall from the grace of God and be eternally lost. It is those that those who do profess faith and then fall away were never in grace.
The Bible teaches the security of the believer, and we need to draw much comfort and assurance from this fact. But the Bible also teaches that a believer may become an unbeliever, that the obedient can become disobedient. Our disagreement is not over whether God is able to do what He promised. The question is, “Can a believer choose to quit obeying God and thereby cease believing?” The Calvinist denies man’s ability to make such a choice, but his conclusions make God a respecter of persons (Acts 10:34-35; Romans 2:11). This denigrates man’s will to the level of a robot. Man is a free moral agent who can choose to believe or to reject, and so long as he lives in the flesh man can change his spiritual condition and eternal destiny (Ezekiel 18:20-24).
In the letters of Timothy, one’s faith can be overthrown (2 Timothy 2:18), one can cast off their faith (1 Timothy 5:12), one can depart from the faith (1 Timothy 4:1), and one can make shipwreck of faith (1 Timothy 1:19). Individuals who turned away include Judas (John 13:2), Simon (Acts 8:12-24), Demas (2 Timothy 4:10; cf. Colossians 4:14; Philemon 24; 1 John 2:15), and Hymenaeus and Alexander (1 Timothy 1:19-20). God is sovereign. By grace He extends salvation to all men. Whether we are saved or lost will be determined by our response of faith. If we do obey, we must be strong or we will forfeit our faith and fall away from God’s grace.