I believe it is because too many that have not been called to preach are representing the church:
1 John 4:1
"Beloved, do not believe every spirit, but test the spirits to see whether they are from God, for many false prophets have gone out into the world."
"I appeal to you, brothers, to watch out for those who cause divisions and create obstacles contrary to the doctrine that you have been taught; avoid them. For such persons do not serve our Lord Christ, but their own appetites, and by smooth talk and flattery they deceive the hearts of the naive."
Also, there are many Christians proclaiming to be saved when they do more cursing and wickedness than most. This does not set a good example of who God is and what He wants for us. God lives within you and the main purpose of the church is to feed the spirit of God in you with Godly teachings.
"But the fruit of the Spirit is love, joy, peace, patience, kindness, goodness, faithfulness, gentleness, self-control; against such things there is no law."