Countering the Protestant claim that "Oral Tradition" was invented to justify unbiblical teachings.

Protestants are understandably concerned when Catholics appeal to "Tradition" when justifying certain teachings. There is a certain objectivity, and thus safety, about having a written document like the Scriptures. Indeed, that's one of the reasons why Catholics believe God gave us the Scriptures in the first place. Too often, appeals to Tradition are framed in terms of "Catholics cannot justify this teaching from Scripture, so they must turn elsewhere," and that "elsewhere" is seen as some secrete list of teachings passed on orally, from one bishop to another, even though nobody knows when or where. If this is what "Tradition" refers to, then this should be troubling to any Catholic. But fortunately, that's not the case, and in fact the answer is deceptively simple: Oral Tradition within historical Christianity is basically synonymous with the Liturgical Life, that is how the Sacraments are celebrated, the Liturgical Calendar, etc. These are very 'public' sources to consult, and more or less objective as well, so there is no hiding things and then randomly appealing to some unwritten unverifiable "tradition" when need be. 

Why Protestants reject the Council of Nicaea.

The Council of Nicaea is a very useful apologetics tool beyond just discussing matters of the Trinity. What most people don't realize is that Nicaea produced more than just a Creed, it also issued 20 canonical laws which were binding on all Christians living at that time. The information contained in these Canons is just as useful (if not more so) as any Church Father when it comes to evaluating Protestantism against the bar of Church history. Below, I will mention why each of the 20 Canons are incompatible with all Protestantism in one way or another. This leaves Protestantism in a significant bind, because virtually all Protestants wholeheartedly affirm the Creed and deem the Council to be an orthodox testimony in early Christianity. After reading these Canons, the Protestant must recognize that they cannot embrace the Creed without also embracing the Canons, because if the Canons teach heresy and error, then the Protestant has no business at all embracing the Creed which this same Council produced. Protestants have no problem affirming the Catholic Church is correct on a lot of things, but they say the Catholic Church is false and cannot be trusted because it also teaches many errors. By this same logic, a Protestant must reject Nicaea as well, for Nicaea teaches many "errors" in its Canons and binds all Christians to these "errors" as well.

Love this quick yet effective refutation of sola fide (which the Protestants didn't see coming).

I think I've come upon a devastating yet subtle 'quickie' argument against the Protestant (especially Reformed) notion of justification by faith alone. Catholics will often point out that "faith that works through love" is what Paul meant when he spoke of the essence of a justified believer (Gal 5:6), and that without love we are told by James that "faith is dead" (James 2:24-26). Protestants think they have an answer for this, by insisting (without proof) that "true faith always comes with love" with it. This seems like a save at first, but thinking about this means the Protestant is saying that when a person receives the gift of faith prior to justification, they also receive the gift of love along with it. That's a problem, and here's why. 

If a person receives faith and love prior to justification, it means the unsaved individual loves God already, prior to even accepting the Gospel message! This cannot be, and thus the Protestant must reject this and say faith doesn't automatically include love along with it prior to justification. This leads to a few significant but plain conclusions:

(1) Faith prior to justification lacks love, and thus this faith must start off 'dead'. This isn't necessarily a bad thing, just an incomplete thing, which is why justification is still needed. 

(2) Justification must be what bestows love, and this seems confirmed by Scripture (e.g. Romans 5:5), and thus the Protestant can no longer say justification is purely forensic, but rather infuses divine gifts into the soul.

(3) Dead faith prior to justification becomes living faith after justification by the addition of love to faith, and herein is the essence of a justified believer. This would mean it isn't Christ's Imputed Righteousness that makes all the difference, but rather the presence/absence of love, and thus suggests your justification (salvation) hinges upon what you do with that love. This is why texts like Revelation 21:8 list "unbelief" as one of the many sins that can damn a person, because it's possible to have faith and be damned by other grave sins.

Given the above, when Paul says we are "justified by faith," he isn't saying we are "eternally saved by faith," rather he's saying that we receive God's love within us by believing in the Gospel, and that this is just the beginning of our salvation (Rom 13:8-14; Gal 5:13-14).

How Protestants completely botch the Biblical teaching on what being "Born Again" means (a.k.a "Regeneration" in Calvinism)

As I looked upon the Catholic Encyclopedia entry on "Regeneration," I was fascinated by what I saw. Below I will quote from the entry, but trim it down for brevity and to highlight some key points:

Regeneration is a Biblico-dogmatic term closely connected with the ideas of justification, Divine sonship, and the deification of the soul through grace. Confining ourselves first to the Biblical use of this term, we find regeneration from God used in indissoluble connection with baptism, which St. Paul expressly calls "the laver of regeneration" (Titus 3:5). In His discourse with Nicodemus (John 3:5), the Saviour declares: "Unless a man be born again of water and the Holy Ghost, he cannot enter into the kingdom of God." The idea of "birth from God" enjoys a special favor in the Joannine theology. Outside the Fourth Gospel (Jn 1:12 sq.; 3:5), the Apostle uses the term in a variety of ways, treating "birth of God" as synonymous now with the "doing of justice" (1 John 5:1, 4 sq.), and elsewhere deducing from it a certain "sinlessness" of the just (1 John 3:9; 5:18), which, however, does not necessarily exclude from the state of justification the possibility of sinning. It is true that in all these passages there is no reference to baptism nor is there any reference to a real "regeneration"; nevertheless, "generation from God", like baptismal "regeneration", must be referred to justification as its cause. Both terms effectually refute the Protestant notion that there is in justification not a true annihilation, but merely a covering up of the sins which still continue (covering-up theory), or that the holiness won is simply the imputation of the external holiness of God or Christ (imputation theory).

Was the 'one bishop per city' model of church leadership an unbiblical corruption by Catholicism? (A brief look at the monespiscopate)

One anti-Catholic argument I'm seeing come up more and more frequently is the claim that Scripture describes church governance (polity) as done by a plurality of elders/bishops who are co-ruling over a city/church, whereas the notion of authority concentrated into the hands of one elder/bishop ruling over a city/church is a later invention. The goal of this anti-Catholic argument is to suggest the office of Papacy grew out from this earlier one-bishop (monepiscopacy) corruption of true Biblical polity.

The Protestant/Liberal argument is basically this: in the New Testament, the term "bishop" ("elder") is always used in the plural, and that it wasn't until AD150 that the monepiscopate (i.e. one bishop per city) model arose in some places. At first, this claim seems to have some plausibility, but looking at it with the right glasses on will reveal the desperation of these Protestant/Liberal folks to do whatever they can to smear Jesus' one and only Catholic Church.

The first thing I noticed about this anti-Catholic argument is that it claims this major heresy arose as "late" as 75 years after the Apostles died, around AD150. It is unlikely that such a significant error would arise that early on, only to be universally embraced by even the great Church Fathers, and nobody to oppose it. Further, this small window of time doesn't leave much room for a fair look at the evidence, since the early Christian writings for this period are minimal. This kind of argument is essentially based on the Liberal/Protestant notion that Christianity as we know it was invented over the centuries by the workings of men, who corrupted Christ's simple teachings early on and invented basically every doctrine we now affirm. If it can be argued that Christianity is a series of inventions, like the monespiscopate, then this leaves Christianity with little credibility before the world. It's sad that Protestants would want to go there, but Liberalism is quite literally an outworking of this kind of Protestant thought. Just looking at the Council of Nicaea in AD325, which historically Protestants pretend to accept when Catholics aren't looking, in Canon 6 it explains there is a head bishop in Alexandria, Antioch, and Rome - the three biggest Christian metro areas. Are these Protestants seriously going to say Nicaea espoused both orthodoxy and heresy? Sadly, many Protestants would rather throw out Nicaea than grant any points to Catholicism. I call this the ABC mindset - Anything But Catholic - wherein an opponent of Catholicism would rather accept the most absurd conclusions (e.g. throwing out Nicaea) rather than admit Catholicism got something right.