When you make a decision to obey the Lord in a particular area, whether it is, tithes and offerings, sexual purity, or any other area. I guarantee you that the devil will come at you with unexpected temptation. In the area of finances, expect to receive, an unexpected; medical bill, car repair. If you decide to be sexually pure, be assured you will be tempted in this area.
If you give into the temptation or decide that now, that you’ve received this unexpected bill and can't afford to keep the promise you made, guess what? Every time you make another promise, be assured that you will face unexpected pressures. Why? Because satan knows all he has to do is throw something unexpected your way, and you will give into it; you will disobey God and go back on your promise.
Better to decide that once a promise is made, you will follow through, no matter what comes your way. And, when you do, it gets easier and easier each time to do so. Why? Because the devil knows this game doesn't work on you, so he will go try it on someone else.
Maybe we should take a lesson from our children. One of the first things children learn to say when they speak in short sentences is "you promise?" Children understand that a promise carries a vow; that it is something that won't easily be broken.