There are many lessons for life that can be learnt from this episode of David. However, one of the most fascinating lessons is the lesson of knowing what it means to have a balanced faith.
Why did David choose 5 stones when he had to use only one?
I've heard sermons that talked about the rest of the stones reserved for the other giants. One can find lessons for his own life from a story; a lesson that speaks to him in his own situation.
But, looking directly at the very stage of the incident, I find one thing very instructive about faith:
Faith is not an excuse for not putting the best of all we can gather into our bag. Faith is not an excuse to say, for instance, that I don't need to learn this or I don't need to concentrate on polishing my skills, or I don't need theology or philosophy or history or geography.... It's unlike a rustic Christian who told to a young man aspiring to get into ministry: "Why do you need to get school education anymore; you're going to be a preacher after all!" You never know which of things that God brings in your path to put into your bag is the thing which God wishes to use to fell the giant ahead of you. David chose the best of the stones that could aim best and he chose as many as he could put in his bag. Thereafter, I think, he left to God the alternative to choose from whichever stone he had filled his bag with.
I think he applied this principle to every facet of his life. He was not just a warrior. He was a musician. He was a writer. He was a statesman. He was a prophet. He was a theologian. He never was ashamed to dance before His Lord though he was a king. It didn't matter to him what the thing at hand was. He gave his best to the Lord. Isn't it reasonable why then he was called a man after God's own heart (Acts 13:22).
Give your best to the Lord; that's the essence of true worship. Then, see what God will do with the small things we've been faithful in.
Prayer: Lord, we thank you for all the things that you bring in our path daily. We thank you for the opportunities you give us to learn and to increase in wisdom and in favor with God and man. We pray Lord that you'll give us strength to excel in the things that we're entrusted with, whether it be studies, job, or housekeeping. And, we pray that the excellency of your power will be manifested in every passing moment of our lives. Amen!