Like most Christians, doubt is a part of my life. I don't know if I struggle with doubt more or less than you, but it's usually not very far away, taking every opportunity to pester me with questions: "Is Jesus really alive? How do you know you're in the right religion? What if none of this is true?"
Ultimately, it's the Holy Spirit alone who can help us fight doubt, because God's Spirit is the only source of doubt-killing faith. But when I reflect on the ways the Spirit helps me in my doubt, there are four aids He often presents to me, four truths that, no matter how deep my pessimism, I just can't shake. I write them here in case they might help you today or sometime soon.
The heavenliness of the gospel - When I begin to doubt whether this Christian faith is the real deal, the amazing and heavenly perfection of the gospel helps me immensely. Every religion and worldview has to provide answers for basic questions: Why are we here? Why are things so bad? What can be done about it? But alone among world religions and philosophies, Christianity is clearly not something made up by mere humans. Whereas other religions are based on various types of good works, the gospel is based on grace. While other worldviews start with me at the center, Christianity exalts God above mankind at every single turn. In all the world religions, we have perfect examples of the types of things humans invent to fulfill the deep desire for religion. But in Christianity, heaven shines as humanity is humbled and God alone is exalted.
The paradoxes of theology - Another difference between Christianity and most other religions and worldviews is the presence of paradoxes within our doctrine. These paradoxes are things that strike us nearly nonsensical at first, but are taught in Scripture as true truths, even if they are too high for us to grasp fully: God is three persons in one God...the incarnate Jesus is fully God and fully man...we are inseparably united to Jesus by faith. These are clearly taught throughout the Bible as truths I can believe even if I can't fully understand. For some, these paradoxes pose a real problem. But for me, they're one of the strongest confirmations that true Christian doctrine must be from God. Religions and worldviews springing from the mind of man are completely comprehensible by man. But if there is a true religion coming to us from God, we would expect it to include truths too high for us to fully grasp.
The unity of the Bible - How amazing is the Bible? Over 31,000 verses, written over 15 centuries by 35 different authors...and yet it still tells one, big, wonderful story about God redeeming a people for Himself. When I struggle with doubt, it helps me to consider the Bible itself, that it's inconceivable such a book could happen apart from divine guidance and inspiration. Or, as put much more beautifully "...the majesty of the style, the consent of all the parts, the scope of the whole (which is, to give all glory to God), the full discovery it makes of the only way of man's salvation, the many other incomparable excellencies, and the entire perfection thereof..." (Westminster Confession of Faith, 1:5). No other book is like this, because no other book has the stamp of heaven all over it.
The testimony of church history - Whether it's the eyewitnesses to Jesus' resurrection recorded in the New Testsament, the undeniably heaven-powered spread of the church around the world, the thousands of martyrs who believed deeply enough to give their lives, or the millions of Christians testifying to the power of God in their own salvation, church history always helps me fight doubt. Along with the beauty of creation, church history is a way to see the hand of God proving Himself to be real and true to all His promises. Even the imperfections of the church throughout history (of which there are many) only further prove the power of God's grace to sustain and build a worldwide movement on the shoulders of fishermen, tax collectors, and lots of very unimportant and sinful people.
What does the Holy Spirit use to encourage you in your struggles with doubt?