I recently was asked this question in an e-mail, and I wanted to share my response. If most of us are honest with ourselves, we'd admit that at some point or another we've also struggled with doubt. Maybe this response would even open up discussions in the comments below. I'd love to hear from ya'll. I'd also like to start answering more of ya'lls questions on here, so e-mail or comment below with some of them.
Doubt is never far from faith’s shoulder.”-St. Augustine
I don’t know if you remember that quote or not, or if I even shared it with you before, but it is often an encouragement to me. I hope it will be to you. For a true believer, I am convinced that doubt—NOT FALSE ASSURANCE—is the more prevalent struggle. If I am in Christ, then the tactic of the enemy will be to convince me that I am not in Christ or to rob me of my joy.
If I am not in Christ, then a sense of false assurance will be more prevalent. An unregenerate person doesn’t deal with doubt, because there is nothing to doubt. Doubt attacks belief, not unbelief.
Additionally, I read Anne Voskamp’s book 1000 Gifts, and she makes a good point in there about a person’s thoughts and emotions. She says that it is impossible to be overwhelmed by more than one emotion at a time. The only way to defeat and drive out a negative emotion is to replace it with a more powerful positive emotion. She makes a solid biblical inference to the emotion of thanksgiving. That one thing will conquer fear and doubt every time. What are you thankful for? You have to ask yourself that question and answer it as an offensive weapon.
Lastly, Matthew 12 is a reference by Jesus to the Pharisees who have just attributed evil works to The Holy Spirit. That, he says, is unforgivable. A believer doesn’t do this. In fact, I like this explanation, by Rick Cornish in a book called “Five Minute Theologian”—
“Concern about committing it reveals the opposite attitude of what the sin is. Those who might be guilty wouldn’t care because they have no distress or remorse over the possibility.”
Hope this helps. I will be praying for you. Continue to fight for truth and rest in CHRIST alone. He is the one who saved us, not we ourselves.