I’ll offer a quick response to your question.
Roughly, you asked the following: Can I explain how the Catholic Church, if it was the church established by Christ as it claims to be, could possibly “backslide” when Jesus made several promises about His Church?
The Catholic Church is not the same church established by Jesus, and presently the true church is a small remnant of people scattered around the world who hold to the historic Reformed faith. (I realize that you, like the Jews in Haggai’s day, will despise the day of small things. You do this to your own hurt.) You should join us–even if you have to worship at home to do so. Scripture uses the symbol of a temple to represent the church (Eph. 2:18-22, and as the church fathers attest). Yet, Scripture often warns of a widespread apostasy in the church (see 2 Thessalonians 2:3ff and 1 Timothy 4:1ff), and Revelation 11:1-3 explicitly teaches that the greater part of the ‘temple’ of God (the outer court) would be filled with wicked Gentiles, while a small part of the ‘temple’ of God (the inner court) represents the true converts. In other words, Scripture forewarns us to expect the larger part of the church will be apostate and opposed to the small remnant of God’s people. You’re in the outer court, my friend.
As for the promises: Christ has and will keep every one of those promises as they are properly understood. First, he promised His Spirit to guide the apostles into all truth. They deposited that truth to us in the sacred Scriptures and in their oral teachings in the apostolic age. Wicked men, however, are capable of wresting the Scriptures, and so, when wicked men gain the ascendancy in the church, it backslides.
Second, the church has the power to bind and loose insofar as it exercises ecclesiastical discipline, resolves theological controversies through authoritative judgments, etc. When it does this in accordance with the truth, then its decisions and acts are bound in heaven. If, however, an evildoer or crew of evildoers presumptuously act as though they have legitimate authority in the church and try to bind the church to their teachings, the only thing bound in heaven is the certainty of divine judgment against those evildoers and those who believe their lies.
Third, hell won’t finally prevail against the church. In fact, in a few short years, we will be reigning over the world and the Roman Catholic Church won’t even exist. (Read the book.)
Fourth, the church is the pillar and ground of truth–just not the Roman Catholic Church. It is the faithful remnant–“two witnesses”–who testify against the sins of the world that uphold the truth against the majority.
–Dan