Technically we can say that such a statement is true. The only way we are in communion with God is through the Holy Spirit, so, yes, the Holy Spirit is he who will keep Christ’s message faithfully with us. But, we must ask, in what manner does he accomplish this task? Is it just through a faithful and sincere reading of holy scripture? Well, first of all, that could not have been true in the beginning for the simple fact that there was no Bible (as we think of it) until the Catholic Church (guided by the Holy Spirit working through Holy Tradition and the magisterium) defined of what exactly the Old and New Testaments consisted. In fact, the decision made by the Catholic Church was not the a foregone conclusion on all fronts: There were books that many people thought would be included that were not and there were books that many people thought would be rejected (such as Revelations) and were not. Consider that alone for a moment. But let’s forget all of this as a mere logical “bump in the road” for a moment (although it certainly isn’t): Let us posit the idea that the Holy Spirit, at some point in history after the Bible was set, began to interact with individuals in the way previously claimed. Now, we need to consider something else: Is the truth of Jesus Christ one truth or many truths? In other words, is Jesus the Truth or the truths? Well, clearly, he is one truth. Then, logically, if the Holy Spirit is to communicate his truth through only medium of a sincere and prayerful soul, then, positing the idea that there are such souls in all denominations and churches in Christendom, which I think is absolutely true, then all denominations and churches should recognize the same truth. Except that such is not the case. If the disagreements were just minor ones, then perhaps a case could be made that this was really so, but, seriously, when the all of Christendom cannot even agree on a canon of scripture, then clearly this is not so. Therefore, we have a contradiction and, consequently, our premises cannot all be true. The only one that is disputable, though, is that the Holy Spirit works in the aforementioned individualistic manner. Therefore, that is clearly not the manner in which he works.
I’m sure you’ve realized by now that this train of logical proof goes on for a quite a bit longer than it already has. Allow me to amend it for the time being and to skip to the part where I posit that the only logical option is that Christ founded an institution (theologically equivalent with a heavenly Kingdom of David) to preserve and proselytize his Truth. Then, obviously, we must discover what that institution looked like in the first century to figure out which one it is now. Anglicanism is not even an option (sadly for the Anglicans), because it wasn’t around in the first century. The only two options for what Jesus Christ’s Christianity looks like (remember, this is if we want to take Jesus Christ seriously and if we want to be logically consistent with ourselves - two things that most people don’t want to do) are then Catholicism and Eastern Orthodoxy.
This then becomes quite easy logically. Let’s look at what both of them profess to be true. Both of them believe in the 4 marks of the Church (this is why the 4 marks were dissatisfying to you earlier - because you hadn’t logically deduced their reliability and necessity). They both believe that Christ’s true Church is One, Holy, Catholic, and Apostolic. Well, both of them have the Holy and Apostolic in the bag. But only Catholicism is One and Catholic. Let’s look at Catholic first. Now, here the word in all its technicalities means “universal,” even though the word had already, by the 2nd century, come to have its modern meaning of “the Catholic Church,” which means, by the way, that the Apostles Creed actually does refer to the Catholic Church and not just a vague “universal church,” although that is besides the point presently. Eastern Orthodoxy is just not universal. Without loss of generality we can notice that there are not many Japanese people in the Greek Orthodox Church. But perhaps there is a clever argument against this. Even if we could posit that the Eastern Orthodox Churches are Catholic, they are, by definition, not “One.” That all goes back to St. Paul’s theology of the “Body of Christ,” by the way, with respect to the 4 marks of the Church. It is very biblical as well as being rooted in tradition.
So, logically, we are left with the Catholic Church being the only option if we are going to take Christ seriously and be logically consistent. To me, if someone reaches this point, then all the minor issues kind of fade away. But, at a later date, since I’m certain you’re tired of reading this by now, I will go into some thoughts on the some of the more specific points you raised.
For now, God bless you and may you have fruitful thoughts!
In Christ,
Sean