Most of the time, growing in faith results from suffering trials.
The Bible addresses this in James 1 ("Consider it pure joy when you face trials of many kinds because the testing of your faith produces perseverance..."), in Romans 5 ("We glory in our sufferings because suffering produces perseverance, character and hope..."), and in 1 Peter 1 ("You greatly rejoice though now for a little while you may have had to suffer grief in all kinds of trials to prove the genuineness of your faith...").
This is not my favorite truth, yet it does seem to be true. Birdsong, blue skies and comfortably full bank accounts produce complacency. Sickness, strife and scarcity drive us to our knees before the Lord. We call out to Him; He answers. We see His hand and thank Him; our faith grows.
We come into this world with hard hearts, with expectations that we are entitled to great blessings, with presumption that we ourselves know what is best for our lives. We come selfishly focused on our own egos, grasping, hoarding, bossing and justifying our every move. Most of us are pretty nasty creatures, without any natural inclination to make sacrifices for the good of others (with the possible exception of our children, but even then we want their benefit for our benefit and not apart from it).
God has to wring the self-idolatry out of us, and in most cases, this requires trials that cause us to suffer. Suffering brings us to the end of ourselves, and coming to the end of ourselves is often what must happen before we become willing to look up to the Lord. "Not my will, but Thine," Jesus prayed in the garden. He prayed it before He suffered, because He was the only sinless, selfless man ever to live. We generally only pray this after we have suffered.
Suffering is the primary way in which God's children grow in faith. However, there are two ways for us to grow in faith without having external suffering thrust upon us. We can grow in faith when we observe the Lord's Sabbath. We can also grow in faith when we tithe.
Observing the Sabbath and tithing are very closely connected. In the first, you are giving to the Lord from the firstfruits of your time. In the second, you are giving to the Lord from the firstfruits of your income. In both instances, you are offering something to the Lord that it may not make sense to give Him, and you are trusting Him to make it up and supply what you need in the end.
The Sabbath is a day of rest that we offer to the Lord because He asks us to. It is one of seven days, a day to set aside as holy to the Lord, a day to cultivate a thankful heart, a day to refrain from the business of providing for ourselves. It is a teacher trusting God with her lesson plans, even if she doesn't chart them out on Sunday afternoon. It is a businessman turning off his phone for a day, ignoring the email, and trusting God that the necessary deals will come through anyway. It is a student putting away his textbooks for the day and trusting the Lord with the results of his exam. It is a farmer parking his combine on Sunday and trusting that God will help him bring in the harvest on Monday, even if rain is predicted (that must be the hardest one of all to follow through, because all the others can--and should--work ahead, but the farmer is truly at the mercy of the weather).
Honoring the Sabbath makes little logical sense. Why would you set aside an entire day of the week when you could be productive? God asks us to do this so we will remember that He is our Creator and Provider. He delights to honor His children when they do this thing to honor Him. If you fellowship in Christian circles, ask around and you will hear wonderful stories about how God has cared for His own when they have honored His Sabbath Day in situations where it seemed like a risk to do so. God comes through. Honoring the Sabbath Day is a practical step we can take, on our own, when we desire to grow in faith.
Similarly, tithing makes little sense. Why would you give ten percent of your money to "the Lord's work"? Why would you do this off the top, before you even know what emergencies will come up before your next paycheck?
People who tithe will tell you that it makes no sense, but the Lord provides. Even when the budget on paper won't balance, somehow when we honor God with the firstfruits of our money, He makes sure that we have enough. Sometimes it seems that while tithing, people have less emergency expenses, while when they fail to tithe, the expenses come like gangbusters and drain savings like a hole in a pocket. Sometimes it is even more mysterious than that. When we trust the Lord with our finances and tithe, He meets our needs in amazing ways that lead us to rejoice and multiply our faith.
As Christians, we need to be growing in faith. Anything that is alive must either grow or atrophy, and our spiritual wellness must not be allowed to atrophy. God loves us too much to ignore us and leave us in complacency, so He consistently brings us faith exercises, or trials, to strengthen our spiritual muscles. However, we can work with Him on this and take some proactive steps of our own to increase our faith. Honoring the Sabbath and tithing are two things we can do from our own initiative to help our faith become stronger.
Has God shown Himself faithful to you, and thus strengthened your faith, when you have honored Him through the Sabbath or tithing? Please share about it if He has.