Think about the kind of faith David had when he picked that stone up knowing he was, with no doubt in his mind, going to slay the giant. He knew God was with him. He knew the giant in from of him would be no longer. Oh what faith he had!
We also can have that kind of faith, taking out the Giants in our life. What is our stone, it’s our faith in God that He is with us and helps us concur any giant (troubles, problems or anything else) that gets in our path, especially the path that leads us to our Lord.
Just remember, even if you start with a pebble (a little faith), when you know the Lord is by your side, that pebble one day can become a rock, which can become a boulder, which can knock down any giant that gets in your path.