One thing I've learned firsthand--and secondhand as I've watched other people--is that the devil is out to get our faith. If he can change our beliefs or get us to back off what we believe, he's won.
Adversity is how he does it. Difficult times. Unexplained things. Things that make you question the reality of who God is. When these things happen, we as humans seem to have the innate reaction to question or blame God because He's all-knowing, all-powerful, and ultimately, shouldn't He be able to stop those things?
Well, this is where it gets confusing for us as humans. Yes, I believe God can ultimately do what He wants, but for some reason, He has created the world a certain way. He created a beautiful world, gave it to Adam to manage, and Adam messed up. He ultimately handed over legal authority of this world to our enemy (and God's enemy) Satan. Satan has the legal right to do bad things on this earth, hence the corruption. God has access to the world through believers and through prayer, and through His Spirit, as He sees fit, but ultimately, we live in a corrupted world.
This is where the test of faith comes in.
When people decide to believe in God and become a Christian, Satan immediately wants to steal that Word from them. It's like the parable of the sower in Mark chapter 4. Seed was sown by the side of the road, but birds snatched it up. It's kinda like ideas about God are sown in someone's heart, but the enemy will snatch them up if at all possible. We are in a battle to keep our faith in an unseen God who is greater and mightier than anything else on earth--but works in mysterious ways and has ways that are much, much different than what we imagine them to be.
James chapter 1 tells us that our faith is what is being tried in all this adversity we face, and I think we see this same importance of faith over and over again throughout the Word.
Why does the enemy want our faith? I think the answer is in 1 John 5:4-5.
"For whatsoever is born of God overcometh the world: and this is the victory that overcometh the world, even our faith. Who is he that overcometh the world, but he that believeth [or has faith] that Jesus is the Son of God?"
The ones who have faith ultimately win.
I believe our faith will pay off in multiple ways between now and the end of the world when God comes to make things right, but there will be times when faith is hard to hold because of what we see. That's when we need to remember to keep faith. The Bible is right, God is good, and He is faithful. No matter what we see, His promises are true, available to you today, and He ultimately wins in the end. I'm glad I'm on His side.