Matt 18:15-20
 If your brother sins, go and show him his fault in private; if he listens to you, you have won your brother.  16 "But if he does not listen to you, take one or two more with you, so thatBY THE MOUTH OF TWO OR THREE WITNESSES EVERY FACT MAY BE CONFIRMED.  17 "If he refuses to listen to them, tell it to the church; and if he refuses to listen even to the church, let him be to you as a Gentile and a tax collector.  18 "Truly I say to you, whatever you bind on earth shall have been bound in heaven; and whatever you loose on earth shall have been loosed in heaven.  19 "Again I say to you, that if two of you agree on earth about anything that they may ask, it shall be done for them by My Father who is in heaven.  20 "For where two or three have gathered together in My name, I am there in their midst." 

The end of the process in verses 15-17 is to take the matter to the church. Verses 18-20 speak about the authority of the church to judge and speak for the Lord regarding such matters. Verses 18-19 are often used to illustrate the effectiveness of prayer, but the primary meaning is about the authority of church leadership.