Assurance of Salvation
Many Protestants believe that once one has "accepted Jesus Christ as personal Lord and Savior", he can be absolutely certain that he will be saved–hence the question most often asked by Protestants: "Are you saved"? The Catholic Church teaches that absolute assurance is never possible in this life apart from a private revelation to that effect. The Church teaches that one can have a moral assurance of salvation–we can be certain that one who dies in the state of grace will be saved. We can be sure that by all indications, according to our fallible human judgment, we are in the state of grace. But we cannot be certain that we are in the state of grace, because grace cannot be sensed.
Paul makes this clear when he writes: "I do not even pass judgment on myself. Mind you, I have nothing on my conscience. But that does not mean that I am declaring myself innocent. The Lord is the one to judge me, so stop passing judgment before the time of his return. He will bring to light what is hidden in darkness and manifest the intentions of hearts" (1 Cor. 4:3-5). Paul often spoke about being a Christian, because by all indications, that is what he was, but that does not mean he claimed to have an absolute assurance of being in the state of grace. Paul said elsewhere: "Therefore let any one who thinks (not "knows") that he stands take heed lest he fall" (1 Cor. 10:12; Rom. 14:4).
Even Protestants must admit that one cannot have absolute assurance of salvation. According to Calvinism, if a member of the Church sins seriously some time after "accepting Christ as his Lord and Savior", it is believed that he was never saved in the first place, although the person may have been completely convinced that he was saved. So no one can really say for sure that he truly "accepted Christ" with infallible knowledge. No one can be sure that his repentance and faith is genuine, that he has turned to God "with all his heart" (Joel 2:12).
This does not mean that we should despair regarding our salvation. We can have great confidence in our salvation (Matt. 7:16; Acts 24:16; 2 Cor. 1:12; 10:7), so we need not despair. Believers must "Test yourselves to see whether you are living in faith; examine yourselves. Perhaps you yourselves do not realize that Christ Jesus is in you–unless, of course, you have failed the challenge" (2 Cor. 13:5). Believers must "test" themselves because they do not have infallible assurance of their salvation. Yes, Paul does say "Christ is in you", but this is an expression of Paul's convictions and strongly held beliefs, his great confidence in their souls being in a state of grace, not his infallible knowledge of their salvation. Just as Paul did, we may say "we are justified," or "we have been saved," or "we are in a state of grace" without presuming to know with absolute certainty, because we believe completely that we are "justified," "saved," and "in a state of grace," and we have great confidence if we have examined ourselves (Rom 8:24; Eph. 2:5-8; 2 Tim. 4:7-8).
"The Spirit himself gives witness with our spirit that we are children of God" (Rom. 8:16). Paul believes wholeheartedly that they are "children of God", and have received the testimony of the Holy Spirit, but he nor anyone else have infallible certitude of their salvation. Of course, since these words are contained in Scripture, they are infallible, and the "we" that Paul refers to were in the state of grace. But no one knew at the time that Paul's words were infallible Scripture, and therefore, did not have an infallible assurance of their salvation. Similar passages such as Colossians 2:2 simply reveal Paul's belief in his salvation or the salvation of others, not his infallible knowledge, which he did not have.
In 1 John 5:13, we read, "I have written this to you so that you may know (eidete–from oida–"to know") that you have eternal life–you who believe in the name of the Son of God." In English as well as in Greek, "to know" can mean assurance, or it can mean great confidence. A student can say, "I know I am going to pass my exam tomorrow," but the fact is, he cannot know this for certain. "Know" in this case means great confidence, based on the fact that he has studied well and knows the material. Therefore, he has a moral certitude. The passage continues: "And we have this confidence in Him, that if we ask anything according to His will He hears us, and if He hears us we know (oidamen–from oida) that what we have asked him for is ours." (1 John 5:14-15; Matt. 21:22; Mark 11:24). Of course, we do not get everything we ask for, so "know" here obviously refers to great confidence once again. John here was assuring believers that they had eternal life. But he was not assuring any of the recipients of his letter that they were in the state of grace. By all indications they were, but such a thing was known only by God.
Only God can know the "hidden things of the heart." Our consciences may be clear, but we are "not thereby acquitted" just because we think we are. We can have the assurance that God will save everyone who is in a state of grace (Zech. 1:3). If we have the gift of faith, have been baptized, and are not in a state of mortal sin, we know that we will be saved. But we can be deceived (Prov. 30:12; Matt. 7:21-23). Our feelings can mislead us: "He who trusts in his own mind is a fool" (Prov. 28:26), and so can Satan. We never really know with absolute certainty that we have truly repented (Prov. 21:2; Jas. 1:22, 26), that we have sincerely accepted Christ with all our hearts: "Who can say, "I have made my heart clean: I am pure from my sin?" (Prov. 20:9). Job said: "If I am wicked, woe to me! If I am righteous, I cannot lift up my head" (Job 10:15), this from a man whose conscience testified to his righteousness (Job. 27:6). Lydia, as a new believer, did not have infallible certitude: "If you have judged me to be faithful to the Lord, come to my house and stay" (Acts 16:15). Only God knows with infallible certitude (Is. 1:16-18; Joel 2:13, 14; Jon. 3:9).
Think about it this way. There are certain characteristics that make someone a true friend. True friends do things for you, they support you, they are trustworthy, they make time for you. But we decide whether or not someone is a true friend based on our fallible human judgment. In reality, the people we think are true friends may spill a secret to other people. Yet this would not stop us from saying "I know you are a true friend." We say "know" not because we have an absolute assurance, but because by all indications, that person is a true friend, and there is no reason to think otherwise, so using the word "know" is appropriate, but only in the sense of great confidence, a moral assurance. Even if we ourselves think we know we are a true friend to others, we might find ourselves divulging a friend's secret to another. That would mean we fooled ourselves into thinking we were a true friend. Similar deception can occur with salvation.