"Not everyone who says to me, ‘Lord, Lord,’ will enter the Kingdom of heaven, but the one who does the will of My Father who is in heaven. On that day many will say to Me, ‘Lord, Lord, did we not prophesy in Your name, and cast out demons in Your name, and do many mighty works in Your name?’ And then will I declare to them, ‘I never knew you; depart from Me, you workers of lawlessness.’"
This passage is one of the most frightening in the New Testament. Will Jesus say of me, “I never knew you”? “The heart is deceitful above all things, and desperately wicked: who can know it?” (Jeremiah 17:9 KJV) – but is my heart so deceitful that I could convince myself that I know Christ, only to hear Him say, “depart from Me”? The answer is yes, it is. But our hope rests in something greater than our hearts.
The gospel teaches that our salvation is secure in Christ. “My sheep hear My voice, and I know them, and they follow Me. I give them eternal life, and they will never perish, and no one will snatch them out of My hand. My Father, who has given them to me, is greater than all, and no one is able to snatch them out of the Father's hand.” (John 10:27-29)
The Westminster Larger Catechism gives a summary of the Bible’s teaching in Question-and-Answer numbers 79 and 80. They are long, and the language is not easy, but it is worth reading them through.
79. May not true believers, by reason of their imperfections, and the many temptations and sins they are overtaken with, fall away from the state of grace? True believers, by reason of the unchangeable love of God, and His decree and covenant to give them perseverance, their inseparable union with Christ, His continual intercession for them, and the Spirit and seed of God abiding in them, can neither totally nor finally fall away from the state of grace, but are kept by the power of God through faith unto salvation.
80. Can true believers be infallibly assured that they are in the estate of grace, and that they shall persevere therein unto salvation? Such as truly believe in Christ, and endeavor to walk in all good conscience before Him, may, without extraordinary revelation, by faith grounded upon the truth of God’s promises, and by the Spirit enabling them to discern in themselves those graces to which the promises of life are made, and bearing witness with their spirits that they are the children of God, be infallibly assured that they are in the estate of grace and shall persevere therein unto salvation.
In other words, we trust in God’s unchangeable love, and not our own changeable hearts; Jesus Himself prays for us, and the Holy Spirit abides in us. They hold us secure, and not our own efforts. We can trust in God’s promises and the Holy Spirit’s testimony that we shall not fall away from Christ.
But how do we know that we really believe in Him? How do we know if we’re deceiving ourselves? Jesus says that those who will be cast away are the “workers of lawlessness.” In fact, this whole section, though applicable in general to all Christians, is also specifically related to the previous section of the sermon on the mount: how to recognize false teachers. “You shall know them by the fruits,” Jesus says. A healthy tree bears good fruit, but a diseased tree bears bad fruit. As trees planted by the living water, we bear the fruit of the Spirit: love, joy peace, patience, kindness, goodness, faithfulness, gentleness, and self-control. The Holy Spirit’s presence bears itself out in our lives.
It is easy to say, and even “believe” the right things. “You believe that God is one; you do well. Even the demons believe—and shudder!” (James 2:19) We absolutely must believe in hearts and confess with our tongues that Jesus Christ is Lord! But faith does not stop there. James also writes, “But be doers of the word, and not hearers only, deceiving yourselves. For if anyone is a hearer of the word and not a doer, he is like a man who looks intently at his natural face in a mirror. For he looks at himself and goes away and at once forgets what he was like. But the one who looks into the perfect law, the law of liberty, and perseveres, being no hearer who forgets but a doer who acts, he will be blessed in his doing.” (James 1:22-25) John too relates the words of Jesus: “If you love Me, you will keep My commandments.” (John 14:15)
This is not to say that our works save us. They do not! But our obedience is a sign that our faith is alive.
This is also not to say that we look to our works for our assurance of salvation. We do not! We look to the Father, who made us His children, and gives us His Spirit.
“See what kind of love the Father has given to us, that we should be called children of God; and so we are… Beloved, we are God's children now, and what we will be has not yet appeared; but we know that when He appears we shall be like Him, because we shall see Him as He is.”
“By this we shall know that we are of the truth and reassure our heart before Him; for whenever our heart condemns us, God is greater than our heart, and He knows everything.”
“Whoever keeps His commandments abides in God, and God in him. And by this we know that He abides in us, by the Spirit whom He has given us.” (1 John 3:1-2, 19-20, 24)
When you suffer doubt and fear, do not look into your own heart, to ask yourself “Am I really faithful? Am I truly sincere? Is the Holy Spirit in me.” Not one of us will ever find total faith and complete sincerity in his own heart. We will only find rest and assurance in the person of Christ. Look to Him, and long for Him.