“For I know the plans I have for you," declares the LORD, "plans to prosper you and not to harm you, plans to give you hope and a future. Then you will call upon me and come and pray to me, and I will listen to you. You will seek me and find me when you seek me with all your heart."

God knows the plans he has for you, and if you're abiding in him, than He will give you a hope and a future. So when you worry that you're useless, you know that you're really not, because God has promised you in that verse that you're not.