Don't you just love this exchange? Here God is telling Moses he's been chosen to go and deliver the Israelites out of Egyptian bondage and Moses asks, "what if they don't believe me?" What did he expect? Did he think God was going to scratch His head and say, "Shucks, I guess I didn't think of that?" This is God asking you to do it Moses, He's obviously going to make sure you're able...

"What's in your hand," was God's response to Moses's concerns, and that's really where I want to focus. God calls us to work for the kingdom, but sometimes we wait around for some miraculous sign or until we feel we're as good as someone else, but God wants us to just go out and use what we have. Remember the feeding of the five thousand? The disciples found a boy with five loaves and two fish and Jesus not only fed all the people but they took up twelve baskets of fragments (see John 6:9-13).

In the parable of the talents (Mat 25), each servant is given a different sum, but each was expected to go out and use what they were given to grow what the master already had. So, it's incumbent upon us to do the same. Do you like to sing? Perhaps you should use that for the kingdom. Do you enjoy fellowship? Use it for the kingdom. Are you knowledgeable in the Word of God? Use that to reach people and bring them into the kingdom of God. The list could go on forever, because each of us has different talents, abilities, likes, and dislikes. Nevertheless, we should all do our part to impact the world around us.
Don't worry about the things you don't have or can't do, that's why we have brothers and sisters in the kingdom. Just like God provided Aaron to be Moses's mouthpiece (Ex 4:14), we can leverage off of each other's talents to work together. The thing God wants you to do is step out and begin using what He's already given you for the benefit of His kingdom...