Have you ever wondered why a God Who created the world and all its splendor with a spoken word, would use people like you and I to accomplish His will? I have considered this many times and asked myself, like the Psalmist, "Who is man that thou are mindful of him?" The answer is rather simple. He can see what we cannot see.
God looks on the heart. This was demonstrated when the prophet Samuel was looking for the man that God wanted to be anointed King of Israel. Samuel came to Jesse's house and young David was not even thought about or considered. It just never occurred to anyone that the prophet would care to see David because they knew that there was no way a boy like David would be God's choice for King of Israel. Boy, were they wrong! Even Samuel was surprised and asked God if He was sure that this was the one. Samuel thought the choice should have been Saul because He looked like the right fellow. God told Samuel, speaking of Saul, "...Look not on his countenance, or on the height of his stature; because I have refused him: for [the LORD seeth] not as man seeth; for man looketh on the outward appearance, but the LORD looketh on the heart." God saw something in David that others could not see. God saw his heart.
Another example is Gideon in the Book of Judges. He himself could not see why God would want to use him to lead His people and to conquer the Midianites. God saw much more in him than Gideon saw in himself. And what about Moses? He was speechless that God had chosen him for the task of leading the Israelites out of Egypt and out of bondage. God knew He could use a guy like Moses.
There are many examples of men whom God used in His word who did not seem usable. The one element that connects each of these guys is that they were humble. God likes to use those who know that they cannot do it on their own. They must know that it is all Him.
He also likes to use those who are the weakest, so that the world will know that He did the work and it was all Him. The world may look at you as a weak and pathetic Christian, but God sees more. They may call you a "Bible Thumper", but God calls you an heir of the King. God sees the righteousness of His Dear Son when He looks at us. (when I say "us", I'm speaking to the saved). The Bible says, "But God hath chosen the foolish things of the world to confound the wise; and God hath chosen the weak things of the world to confound the things which are mighty;" Remember He sees us differently sometimes than we see ourselves. He wants to show Himself strong to the lost world. He wants the glory for using those who are unusable. "For the eyes of the LORD run to and fro throughout the whole earth, to shew himself strong in the behalf of [them] whose heart [is] perfect toward him" It is so others will see His glory.
If you want to be used of God, be humble and remember that is is all about Him. And next time you start to feel like God cannot possibly use you because of your inabilities or because of your past, because you are too "broken", just hold on because He is ready to do a great work through you!