The question you raise is one that troubles many sincere souls, and rightly so, for the line between a struggling saint and a self-deceived sinner can appear thin to human eyes. Yet the spiritual world is not as the physical, where two plants may look alike but one has a deadly root. Here the root is the heart, and God sees it, but He has also given us fruits by which to judge, that we might not be utterly blind.
First, mark well: a true Christian may be overtaken by a besetting sin, yet he does not make peace with it. He hates it, he groans under it, he struggles as a man chained against a wall strains to break free. When he falls, he does not lie there content; he rises quickly by confession and tears. Consider the words of the apostle: the fruit of the Spirit is love, joy, peace. Now a man fighting a sin may have little outward joy for a season, but look deeper: is there a love for God that mingles with sorrow? A longing for holiness, even when he fails? Does he, like the prodigal, come to himself and say, “I will return to my Father”? That inward turning, that hatred of the sin even while committing it, that resolution after each fall, however weak, to amend, these are the gasping breath of a living soul. Manasseh filled Jerusalem with blood and idols, yet when he repented, the Lord heard him. Why? Because his repentance was not a mere fright at punishment but a loathing of the evil itself. He turned from it with his whole heart.
But the false professor, the one who cries “Lord, Lord” and yet works iniquity, shows a very different pattern. He sins willfully, deliberately, without the violent conflict of the inner man. He may speak well, attend church, and have a form of godliness, but when sin presents itself, there is no wrestling, only a ready consent. He does not flee to God for deliverance; he excuses himself, makes provision for the flesh, and returns to the vomit as a dog with no sense of shame. His repentance, if it ever appears, is worldly sorrow only, like Judas, who felt remorse but ran not to Christ for mercy. He ran to the rope instead. Why? Because the devil, having lured him into the sin, hurried him out of repentance before any fruit could be gathered. True repentance abides and produces amendment; false repentance is a brief spasm that changes nothing. And what says the apostle? “If we sin willfully after we have received the knowledge of the truth, there remaineth no more sacrifice for sins.” This is not a word to the weak struggler, but to the one who, after full light, kicks against it and chooses sin with a high hand, treating Christ’s blood as a light thing. Such a one holds the truth in unrighteousness and makes grace a license for uncleanness.
You ask, is it possible to tell the difference? To some extent, yes, by their fruits over time. A man may stumble often, yet if he keeps rising, keeps confessing, keeps seeking help from the brethren and from the Spirit, his course, though battered, is toward life. His faith, though weak, produces some works of love and charity. His sorrow is not for being exposed but for offending God. The other man bears no lasting fruit. He may have the green leaves of profession, but when the heat of temptation comes, he withers, or he produces thorns where grapes should be. He is not humbled by his falls; he grows harder and more secretive, hiding one sin with another, as Herodias thought to silence John yet only magnified her crime. Sin hidden by more sin stinks to heaven. The struggling saint, however, brings his sin into the light, confesses it, and wages open war against it.
Yet be careful not to sit in the judgment seat reserved for Christ alone. Some men’s sins go before them to judgment, and some follow after. What concerns you most is your own soul. Examine yourself whether you be in the faith. Do not let the delay of vengeance breed presumption, as though God’s silence were approval. That delay is meant for you to gather the fruit of amendment. If you are the struggling one, take comfort: the very fact that you groan and wrestle is proof of the Spirit’s life within you. A dead man feels no battle. But if you are the sinner at ease, who says, “I am rich and have need of nothing,” tremble, lest the fiery indignation that devours the adversaries come upon you also. For if a tree that has been watered and tended yields no fruit, it is pulled up by the roots and given to the flames.
Therefore, let all strive to show forth a conversation worthy of the gospel. Let the fruit of the Spirit be manifest: love, peace, goodness, righteousness, truth. These are not the garments an impostor can wear for long. As gold is tried in the fire, so the human heart shows its metal in the furnace of temptation. The one who endures, who repents, who clings to Christ even weeping, though he be but dust, is of the true household. The one who falls and never fights, who repents not, who hardens his neck, let him fear, for there remaineth no more sacrifice, but a fearful looking for of judgment. May the Lord grant us all a true and working repentance, that we may not fall into the hands of the living God.
Prayer Focus: God, Thank You for loving me. Thank You for loving me, Jesus. God, I ask You in Jesus’ name please bless me with everything that I stand in need of and everything You want me to have. 
