I know of few Christians who backslide instantaneously. No! Usually it happens gradually over a long period of time. Most do not intend to do depart from the faith, nevertheless, they do just the same.
“Take heed brethren, lest there be in any of you and evil heart of unbelief, in departing from the living God” (Heb. 3:12). Some people think a child of God cannot depart but they are wrong. Actually those who think one can fall from grace are the ones who have yet to obtain that grace. Paul warned the Galatians about keeping the law of Moses by saying, “You have become estranged from Christ, you who attempt to be justified by law; you have fallen from grace” (Gal 5:4). God did not warn us of something which is impossible for us to do.
It first begins by missing an occasional service. Then they stop their personal study of God’s Word. Little by little they stop showing up to worship God (Heb 10:25). Then they are drawn away after their own lusts and desires (Jam 1:14).
We are exhorted to give the more earnest heed to the things which we have heard, lest we should let them slip (Heb. 2:1). Therefore, study God’s Word earnestly (2 Tim 2:15). Search the scriptures, making sure what you hear is contained in the new testament (Acts 17:11). Is any suffering, let him pray. Is any merry, let him sing praises to God (Jam 5:13). Love God’s Word and obey it faithfully (2 Thess 2:10 f; Jn 14:15). Prove God’s Word by God’s Word (1 Thess 5:21). Defend God’s Word (Phil 1:17). Contend for the faith (Jude 18). Put on the whole armor of God (Eph 6:11-18). Don’t go beyond that which was written in the scriptures, speaking the very words of God (1 Cor 4:6 f; 1 Pet 4:11) Above all, practice what you preach (Rom 2:15,16).
Christians must be on guard against carelessness and indifference lest Satan gain the advantage and overthrow their faith (2 Cor 2:11). “Be sober, be vigilant; because your adversary the devil walks about like a roaring lion, seeking whom he may devour. Resist him, steadfast in the faith, knowing that the same sufferings are experienced by your brotherhood in the world (1 Pet 5:8,9). Christians are soldiers of Christ, therefore, fight the good fight of faith and lay hold on eternal life (1 Tim 6:12 f; 2 Tim 2:2).