When you have repented dozens or even hundreds of times over the same sin and then go back and do it again, it can be powerfully demoralizing to your heart. You may think, "Why am I like this, how can I be genuine if this is how I behave, surely I am lost."
Dear friend, realize that the pain and struggle you feel over your sin is the very evidence that you are God's preciously loved child; for the heathen would never concern himself over his sin, in fact it is impossible for a person to mind sin at all without the power of the Holy Spirit bringing conviction in our lives. But by being torn up about it, you prove to yourself that you truly love God, because the sin so grieves your soul.
"But if I do the very thing I do not want, I agree with the Law, that it is good. So now, no longer am I the one working it out, but sin which dwells in me. For I know that nothing good dwells in me, that is, in my flesh; for the willing is present in me, but the working out of the good is not. For the good that I want, I do not do, but I practice the very evil that I do not want. But if I am doing the very thing I do not want, I am no longer the one working it out, but sin which dwells in me."
Romans 7:16-20 (LSB)
We know that we must forgive others numerous times, if their repentance be true, as Jesus said "Forgive them seventy times seven," the intention being for us to continue without limit. But can we manage to forgive ourselves too; for if we are holding ourselves guilty, does this not make us a usurper of God's judgement? Did He not declare that we are cleansed of our sins, did not the Lord say, "It is finished"? And so let us apply the same grace and mercy unto ourselves that we apply to our brothers and sisters. Yes it feels hard to realize you have repented so many times before for the same thing, but that does not make the next time any less genuine, if it comes from your soul's deepest longing. Do not hold yourself guilty for that which God has already forgiven, consider Acts 10:15, "What God has cleansed, no longer consider defiled."
We must always remember that what we do and feel only consists of second causes; but we are saved and made right with God through the first cause- He drew us in and caused us to be His children, whom He dearly loves (Ephesians 1). Surely in the end He will deliver us; for God is good, without exception. He is faithful and just, and sure to finish the work He began in us (Phillippians 1).
"He saved us, not by works which we did in righteousness, but according to His mercy, through the washing of regeneration and renewing by the Holy Spirit, whom He poured out upon us richly through Jesus Christ our Savior, so that having been justified by His grace, we would become heirs according to the hope of eternal life."
Titus 3:5-7 (LSB)
If it relied on our own power, I daresay we could not remain in grace for even a single day; but blessed be our God, for it relies solely on His strength, faithfulness, and love for us. God is the one who justifies, who then will condemn us?
"But in all these things we overwhelmingly conquer through Him who loved us. For I am convinced that neither death, nor life, nor angels, nor rulers, nor things present, nor things to come, nor powers, nor height, nor depth, nor any other created thing, will be able to separate us from the love of God, which is in Christ Jesus our Lord."
Romans 8:37-39 (LSB)
Mr. Fearing Comforted (Text) by Charles H. Spurgeon
A complete transcript of Charles Spurgeon's sermon about doubts, anxiety, fears, and faith. Centered on Matthew 14:31.
Mr. Fearing Comforted (Audio) by Charles H. Spurgeon
An audio version of the same sermon. Much of this article was heavily inspired by having listened to this sermon the night before; which would explain the particular phrasing I used at times as I wrote it.