I was baptize over forty years ago, and in the ensuing years I have fallen away and came back to the church numerous times. My question is if a person has been truly converted will he or she never fall away and become unfaithful? Is the reason I have been unfaithful to the Lord so much is because I wasn't truly converted in the first place. Thank you.
I have no idea why your faith has not been stable, though there are a few passages that might give a clue. Paul in Ephesians says that a person who does not grow in Christianity is unstable. "For the equipping of the saints for the work of ministry, for the edifying of the body of Christ, till we all come to the unity of the faith and of the knowledge of the Son of God, to a perfect man, to the measure of the stature of the fullness of Christ; that we should no longer be children, tossed to and fro and carried about with every wind of doctrine, by the trickery of men, in the cunning craftiness of deceitful plotting, but, speaking the truth in love, may grow up in all things into Him who is the head -- Christ" (Ephesians 4:12-15). So if you did not spend time becoming knowledgeable of God's teaching you would have left yourself as "ripe pickings" for Satan.
James points out another problem. "But let him ask in faith, with no doubting, for he who doubts is like a wave of the sea driven and tossed by the wind" (James 1:5). If you never become sure about what you believe then again it is easy for Satan to undermine your faith.
But being a Christian has never been a guarantee that you won't fall away. There are so many warnings in the Bible about that very thing. Peter said, "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" (I Peter 5:8). Why the need to be sober and vigilant if the truly converted cannot fall away? As Paul also warned, "Therefore let him who thinks he stands take heed lest he fall" (I Corinthians 10:12).
You were unfaithful because you found things in the world more appealing than following God at the time. Fortunately, they haven't held you captive. But it isn't the past that is important. Today and the future are what matters. "Brethren, I do not count myself to have apprehended; but one thing I do, forgetting those things which are behind and reaching forward to those things which are ahead, I press toward the goal for the prize of the upward call of God in Christ Jesus" (Philippians 3:13-14). Yes, you fell. You're just as weak as the rest of us. But learn from the mistakes. Fill in the gaps, strength the weak areas, and grow as a child of God. There is work to do, and time is slipping away for all of us.