When Jesus told us to be holy, He wasn't saying to be perfect. We can't be. He was telling us to be set apart for God's purposes.

"How, then, can they call on the one they have not believed in? And how can they believe in the one of whom they have not heard? And how can they hear without someone preaching to them?" - Romans 10:14

God can use anyone.

You did not choose me, but I chose you and appointed you that you should go and bear fruit and that your fruit should abide - John 15:16