Can a child of God, a Christian, fall away and be lost. The bible seems to be of that persuasion. Take note of the things a child of God can do:
He can fail of the grace of God (Heb. 12:15). He can be led away with the error of the wicked (2 Peter 3:17). He can err from the truth (James 5:19). He can turn aside after Satan (1 Tim. 5:15). He can fall from steadfastness (2 Pet. 3:17). A weak brother can perish (1 Cor. 8:11). He can forsake the right way (2 Pet. 2:14-15). He can turn from the Holy Commandment (2 Pet. 2:21). He can fall into condemnation (James 5:12). He may be a castaway (1 Cor. 9:27). He may be cast forth as a branch and be burned (John 15:1-6). He may become neither hot nor cold (Rev. 3:14-18). He can be spoiled through deceit (Col. 2:8). He can be moved away from the hope (Col.1:23). He can deny the Lord that bought him (2 Pet. 2:1).
A Christian can do despite unto the Spirit (Heb. 10:29). He can depart from the living God (Heb. 3:12). He can come short of the promise (Heb. 4:1). He can believe the gospel in vain (1 Cor. 15:1-3). He can fail to keep himself in the love of God (Jude 21). He can count the blood of Christ wherewith he was sanctified unholy (Heb. 10:29). He can depart from the faith (1 Tim. 4:1). He can be carried away with strange doctrines (Heb.13.9). He can be beset by sin (Heb. 12:1). He can draw back unto perdition and not save his soul (Heb. 10:38-39).
A Christian can fall after example of unbelief (Heb. 4:11). He can become worse than an infidel (1 Tim. 5:8). He can refuse him who speaks from heaven (Heb.12:25). He can have an evil heart of unbelief (Heb. 3.12). He can trod under foot the Son of God (Heb.10:29). He can fall from grace (Gal 5:4).
Conclusion: If a Christian couldn’t fall away and be lost, then why is faithfulness unto death a requirement for a crown of life (Rev 2:10)? If one could not fall away, then why did Paul warn all Christians to examine themselves whether they be in the faith unless they be disqualified (1 Cor 13:5)? If Christians can’t be lost, then why will there be a falling away (2 Thess 2:3)? The false doctrines of men may profess to those ignorant of the scripture “Once saved, always saved”, but God’s Word is definitive to the contrary. Yes, a Christian can fall away and be lost! Make sure that someone isn’t you by your faithfulness to the doctrine of Christ, your willingness to worship God in spirit and in truth, and your endurance to trials and persecutions (2 Jn 9 ff; Jn 4:23,24; Jam 1:12).