A double minded man is unstable in all his ways.
JAMES 1:8 NASB
I have weak faith. I admit this fault in order to remedy it because I am ashamed of it. I think St. Peter spent the rest of his life remembering and doing penance for the time he gave in to fear and denied his Lord. Likewise, I think I will spend the rest of my life remembering how I turned from faith to embrace atheism. Doubt is always pecking at my brain, and it leads to double mindedness. The result is the instability that James mentions in his epistle.
My hero in faith is my wife who has more reasons than I to doubt the existence of God and His goodness. Yet, she is strong where I am weak. I suspect that this is why God put us together. Everything that follows is her advice on having faith.
There is never going to come a time in your life when you have it all figured out or when it all makes sense. Likewise, seeing is not believing because we know of the many who have seen and refused to believe. You can spend the rest of your life trying to get to some point where there are no doubts and mysteries, but this state of mind does not exist in this world. Even John the Baptist had to send a messenger and ask if Jesus was the real deal.
Faith is a decision. You set it and forget it. Faith is not complete understanding because we are not capable of complete understanding. Faith is believing that God is good, and He will make it all work out in the end. Our task is to stop questioning God's goodness and to simply trust in Him. Doubt must be eliminated as an option.
I have always built my life on the sand, so it crashes on a regular basis. My wife built her house on the rock, and this is why I envied her when I met her. She has faith. She is stable where I am double minded.
Faith is not to be simple minded. Faith is to be single minded. As someone who has been down many avenues of doubt, I realize that St. Augustine was right. Faith precedes understanding. My wife pointed out something to me that I realize was very true. Atheism and mental illness are often found together. You would think that people who believe in angels and demons and God Almighty would be off their rockers, but I find sincere Christian people to be very well adjusted people. Conversely, the atheists I met while an atheist were all nuts. I never met an atheist who had it together.
Faith makes you better. Doubt makes you worse. As someone who has had both, I can attest that the path of faith is the better path. The discipline of faith is to decide to stick to the path of faith no matter what comes. Cross the bridge from doubt to faith then burn that bridge forever. Be single minded in your devotion to God. Faith is a decision, and it is the best decision you will ever make.