The Bible is filled with countless examples where God uses ordinary people to do some pretty extraordinary things. Feats that, without God's help, were impossible according to the world's opinion.  The disciples were just normal men before Jesus invited them to follow and learn from Him, and after Jesus went to Heaven, He used them to carry on His mission to save the world. David was just a young, small shepherd boy who God used to defeat the Philistine giant Goliath. Moses was a murderer with a speech problem who confronted Pharaoh and led God's people out of slavery in Egypt.  Paul was a religious zealot before being transformed by an encounter with Jesus, going on to become a church planter who wrote much of the New Testament.  Peter denied Jesus three times the night of his crucifixion, but would later repent and become a prominent leader in the early church.  

We can't use our past as an excuse to why God would never want to use us. We can't use the excuse that we have nothing to offer. By looking at how God redeemed and used all of these ordinary, broken people to do such amazing acts, we can be confident that He can do the same with us.