The ultimate and most effective Catholic apologetics argument against Protestantism.

I have come to the conclusion that the most powerful apologetics argument that a Catholic can make against Protestantism is that their Sunday Liturgy is actually man-made and thus blatant idolatry. Let me explain this more.

The most important duty a human has, regardless even of whether they are a Christian or not, is to worship God. This should be - without a doubt - an obvious truth that everyone can agree upon. Given this, a person must not only worship God, they must do so properly, i.e., they must worship as God has instructed them to do. This means that Liturgy requires divine revelation, because otherwise the person is "worshiping" God based on what sounds good to their human mind...but there is a word for worshiping according to what sounds good to you: it's called idolatry. So the only way to escape idolatry is to worship according to how God has divinely revealed it. Which leads us to the key problem which all Protestants face.

A powerful OT foreshadowing of the Papacy.

A friend of mine pointed out an amazing Old Testament foreshadowing of the Papacy that I'd like to share (and I think it's as important as Isaiah 22:22-23). The passage comes from the conclusion of Genesis, where the Patriarch Jacob (later renamed "Israel," Gen 32:28) was on his deathbed and giving each of his 12 sons (the Twelve Tribes of Israel) a specific blessing. When it came to his son Judah (Genesis 49:8-12), this is part of what Israel said to him:

Judah, your brothers shall praise you; your father's sons shall bow down before you. The scepter shall not depart from Judah, nor the ruler's staff from between his feet, until tribute comes to him; and to him shall be the obedience of the peoples.

Here Jacob (Father Israel) predicts that the Tribe of Judah would one day come to lead the Twelve Tribes of Israel. As you can probably guess, a Catholic should see a parallel here for the Papal Office, with Peter being one of the Twelve Apostles being selected to be the leader of the other Apostles.

Some might object that if an OT image is not explicitly called out in the New Testament, then the OT image cannot really be said to be a prefigurment/prophecy. But this "rule" simply isn't valid, for the Early Church Fathers were steeped in OT typology, and even though texts such as Genesis 3:15 are never directly quoted in the New Testament, nobody would deny this text is the Proto-Evangelium (i.e. First Gospel). And given that the Twelve Apostles are most certainly premised on the prefigurement of the Twelve Tribes (Matt 19:28; Rev 21:12-14), the notion that there would be other prefigurments is not at all a stretch. 

Another parallel to note is that even after the united 12 Tribes later fell into sin, idolatry, and broke into two kingdoms (the Northern Kingdom of Israel and the Southern Kingdom of Judah), it was clear that God's favor and chosen kingly lineage still remained with Judah (Micah 5:2; Rev 5:5). From this analogy we can gather that even if a Pope were to fall into sin, this in no way entails the Papacy somehow loses it's authority or that schism is ever justified. It was no accident that Saint Paul told the Holy Roman Church, "The God of peace will soon crush Satan under your feet." (Rom 16:20; cf Gen 3:15)