Let's see the whole thing, Matt 18:15-20-
"If your brother sins against you, go and show him his fault, just between the two of you. If he listens to you, you have won your brother over. But if he will not listen, take one or two others along, so that 'every matter may be established by the testimony of two or three witnesses.' If he refuses to listen to them, tell it to the church; and if he refuses to listen even to the church, treat him as you would a pagan or a tax collector.
"I tell you the truth, whatever you bind on earth will be bound in heaven, and whatever you loose on earth will be loosed in heaven.
"Again, I tell you that if two of you on earth agree about anything you ask for, it will be done for you by my Father in heaven. For where two or three come together in my name, there am I with them." The first part of the passage you are refering to regards disputes involving transgressions.
Post #478 is relevant to how Christians should handle transgressions and explains the second part of the passage here. This passage is not to be taken in a vacuum. There is no reference to disputes involving the truth. The truth relevant to the question at hand, can only be found by referencing the scriptures. In particular, the Gospels, because they contain the words of Jesus directly, given by those that knew Him.
"Since the Church alone is mentioned as THE pillar of truth, then It alone has the right to discern the truth and interpret Scripture."
The right to truth belongs to everyone. God's gift of life, intellect and Free will to each individual demands others respect that gift. That means that each man has the right to determine what is, and what is not truth. There is only one unique truth. The church does not hold it necessarily, else Matt 18:19-20 and the promise of the Sign of Jonah would be meaningless.
Matt 16:13-
When Jesus came to the region of Caesarea Philippi, he asked his disciples, "Who do people say the Son of Man is?"
They replied, "Some say John the Baptist; others say Elijah; and still others, Jeremiah or one of the prophets."
"But what about you?" he asked. "Who do you say I am?"
Simon Peter answered, "You are the Christ, the Son of the living God."
Jesus replied, "Blessed are you, Simon son of Jonah, for this was not revealed to you by man, but by my Father in heaven. And I tell you that you are Peter,[rock] and on this rock I will build my church, and the gates of Hades will not overcome it. I will give you the keys of the kingdom of heaven; whatever you bind on earth will be bound in heaven, and whatever you loose on earth will be loosed in heaven." Then he warned his disciples not to tell anyone that he was the Christ.
God came to teach. He said in Matt 7:24,
"Therefore everyone who hears these words of mine and puts them into practice is like a wise man who built his house on the rock."
Peter is doing just as God requested all to do. To build their spirits on His words, a rock foundation that leads to life. His words are found in Scripture and in the Sign of Jonah. Notice the same binding and loosing is that which all will do, according to how they pray and choose. Post #478.
Mark 9:38-40 "Teacher," said John, "we saw a man driving out demons in your name and we told him to stop, because he was not one of us."
"Do not stop him," Jesus said. "No one who does a miracle in my name can in the next moment say anything bad about me, for whoever is not against us is for us. I tell you the truth, anyone who gives you a cup of water in my name because you belong to Christ will certainly not lose his reward.
Yes ... let's do!
"I tell you the truth, whatever you bind on earth will be bound in heaven, and whatever you loose on earth will be loosed in heaven. "
Our Lord instituted the Sacrament of Penance on the day of His Resurrection when He entered the Upper Room and gave the Apostles the power to remit sin by saying: "Receive ye the Holy Ghost; whose sins you shall forgive they are forgiven; and whose sins you shall retain they are retained."
The present-day priest or minister has the God-given right to forgive men's sins or hold them bound for God. Would not the Christian church have died out with the last apostle if these "gifts from God" were not passed on to the present-day clergy through Apostolic Succession?
"God never threatens the repentant, rather He pardons the penitent. You will say that it is God alone who can do this. True enough, but it is likewise true that He does it through his priests, who exercise His power." - St. Pacianus of Barcelona (4th century A.D.)