God uses broken people so that it is indisputably evident that it is a supernatural work and He alone receives the glory.
David was an adulterer, yet God said he was the apple of His eye, favored above all others.
Moses was a murderer and stuttered, but he was called to deliver a nation from bondage.
Paul persecuted Christians to the point of death, but the Lord Jesus met him on the road to Damascus. He wrote the epistles and brought the gospel to the gentiles.
God uses imperfect people to confound the wise- those who think they know everything. He is the great Strategist.