
Simple answer: God tests our faith, primarily through difficulties.
Pain, trials, challenges, sickness are all used by God to test our faith.
Please note I did NOT say God causes hardships to fall on His people; however, He uses hardships to test our faith.
The enemy wanted to harm His people, but God...
"You intended to harm me, but God intended it for good" (Genesis 50:20)
He tested the faith of the ancient Israelites by allowing them to go through hard times in the wilderness, "in order to know what was in your heart" (Deuteronomy 8:2)
Remember, if our faith is weak, it may not be obvious when life is going smoothly and we aren't challenged in any way. When hard times come, a weak faith will be revealed for what it really is: shallow and unable to help us through life's difficulties.
It may be anything: an unexpected illness like ALS, the death of a loved one, the loss of our job, or even a friend who turns against us. When hard times come, the true nature of our faith will be revealed.

So far He has told me HOW he tests our faith. Ok, got it, but, I asked, "Why do you test our faith?"
I mean, He knows my heart so WHY test us?
The answer was like a lightning bolt.

Wow. He is soooo right (Duh!)
We only realize our strength in times of difficulties.
Here I am, in the middle of a spiritual war, having my faith increased. He is with me through this test, but it is a test for me.
Even though the enemy is using ALS to hurt me, God is using it to kick the enemy's ... tail!
None of us likes to go through hard times; but God can use them to show us our weaknesses. We are being prepared for an unrelenting enemy. An enemy that wants to take us all down. God wants to make us strong, if you let Him.
As for me, I am in the fight of my life. Everyday a new challenge; but, everyday I grow spiritually stronger.

"Come on Satan, is that all you got?"
(James 1:2, 4)