“But if I tarry long, that thou mayest know how thou oughtest to behave thyself in the house of God, which is the church of the living God, the pillar and foundation of the truth.” 1Tim 3:15
“Here Christ says, and Paul reaffirms, that the Church will always teach the TRUTH.
Actually, Paul does not say what you claim. He says the Church is the pillar and foundation. There are many times in history where churches have gone into error.
Heresies were dealt with from the beginning of the Church, and the Church has dealt with those introducing false teachings through the ages.
Paul warned us this would happen, "For the time will come when men will not put up with sound doctrine. Instead, to suit their own desires, they will gather around them a great number of teachers to say what their itching ears want to hear. They will turn their ears away from the truth and turn aside to myths." (2 Tim. 4:3–4).
Martin Luther was one of these men Paul warned us about. He so wanted to believe in his view of salvation by faith alone that he tried to remove James from the Bible. "You see that a man is justified by works, and not by faith alone." James 2:24. You have to go through mental and verbal gymnastics to say the clear language of the Bible does not really say what it really says. This is one reason the Catholic Church protected the Bible in the early days. A hand written copy would be guarded as a treasure because of its rare nature, but more importantly to prevent false copies from circulating and supporting heresy.
Fortunately, we have Christ’s promise that heresies will never prevail against the Church. They will arise, endure sometimes for centuries, like Protestantism, but we can be confident in Christ’s promise that the Church will always teach the Truth.