While many wonder what the big deal is between Protestantism & Catholicism, or what the differences are between denominations within Christianity, the issues that produced these divisions, while grounded in history, are still relevant today.  Many lost their lives in the struggle to defend what they understood to be non-negotiable doctrines (teachings) from Scripture.  The very term "Protestant" comes out of the Reformation period to denote those who protested against the Vatican & its teachings.  The official Reformation began on Oct. 31, 1517, when Martin Luther nailed his Ninety-five Theses against the Catholic Church to the Castle Church door in Wittenberg, Germany.  Luther's protest against the many unbiblical doctrines of Catholicism reached its height with the sale of indulgences by the priesthood at the time - an unbiblical practice of selling "permission slips", or absolution for sinful acts yet to be committed.

Prior to Luther, Calvin, Zwingli, & other Reformers (those who sought to reform the church from its apostasy & movement away from biblical foundations) of the 16 C, seeds of the Reformation can be traced back to the 13th - 14th C & perhaps beyond.  Men like Jon Hus, John Wycliffe, & other forerunners to the official Reformation were pushing for the same principles:  A definitive move doctrinally & practically back to the authority of Scripture & away from unbiblical Popish dogma, and a desire to place the Word of God into the hands of the common people in their own language.  Standing firm on these two principles meant the execution of many faithful men by the Vatican over centuries.  While many today think that the Vatican II Council (1962-65) ended the condemnation of Protestants imposed by the Catholic Council of Trent (1545-63) as heretics & infidels, it in fact did not.  Rather, Vatican II affirmed the condemnation ("anathema" or damnation) of all "separated brethren" (believers outside of the Catholic Church).  Simply softening the wording did not remove the proclamation by the Vatican that anyone outside of the Roman Catholic system is damned according to its dogma.  So, we are reminded that while doctrine divides, it also unites & as the apostles told us in Scripture, we are to hold fast to the doctrine delivered once & for all to the church.  The following abridged outline of Catholicism should provide a basic framework with which to build a general understanding to the differences between Protestantism & Catholicism.

I. AUTHORITY: It's in the foundation of authority that we find the foundational difference between Catholicism & Protestantism.

• Protestantism: Singular authority - from the Word of God alone. All teaching, belief, & practice come from Scripture alone.
• Catholicism: Dual authority - from the Bible & tradition. "Tradition" equates to the teachings of the Vatican which in practicality supersedes the Bible & contradicts it in many ways.
• The Apocrypha: Books added to the Catholic Bible by the Council of Trent in 1546, but not included in the Protestant canon of Scripture. (Canon - "a measuring reed", or "standard").

Notes on The APOCRYPHA: (hidden / esoteric books). Sometimes combined with other refuted books & known as the Pseudepigrapha, or "anonymous autographs" by Protestants. the Apocryphal books were added to the Canon by 53 Catholic bishops at the Council of Trent in 1546.  The Apocryphal books were mostly written in the time period of the Old Testament, & were discarded as erroneous by most early Christians, as well as the Palestinian Jews, adding doubt as to the validity of the writings. In addition to these historical facts, we include the following:

      a) Jesus & the apostles never quoted from, nor recognized any Apocryphal book; although they quote heavily from the Old Testament, thereby verifying the Hebrew canon as God's Word.
    b) Josephus, the noted Jewish historian, gives a list of the books of the Jewish Law & Prophets, yet he does not include any Apocryphal book in this list.
     c) The Apocrypha was also rejected by these Church Fathers: Origen (considered by many to be the most learned man in the church before Augustine); Tertullian (scholar of the early 3rd C); Athanasius (orthodox spokesman at the Council of Nicea); and Jerome (translator of the Latin Vulgate which became the authorized version of the Roman Catholic Bible).
    d) The Apocrypha contains historical, chronological, & geographical errors.

II.  THE PRIESTHOOD: The Scripture speaks of the priesthood as fulfilled in Christ, thereby rendering a human priesthood invalid.  Ref: Hebrews 7:11-13, 18-19 & 24; 8:7; 9:11-12, 24-28; 10:10-21.Revelation 1:6.

~Catholicism has more in common with Old Testament Judaism in practice than it does New Covenant Christianity. From the mass to penance, it shadows Judaism in bringing sacrifices to the temple priest for a temporary sin covering as in the Old Covenant.
~Priest: An office appointed by God to be man's representative before Him. A priest brings man into the presence of God.  Protestants reject the Catholic priesthood as biblically invalid.
Quote from a book with the imprimatur of the Archbishop of Ottawa, Canada:  "Without the priest, the death & passion of our Lord would be of no avail to us".  

III. THE MASS & EUCHARIST: Contrast Catholic teachings below with the verses from Hebrews cited above concerning the priesthood:

• New York Catholic Catechism: "Jesus Christ gave us the sacrifice of the Mass...a visible sacrifice which continues His sacrifice on the cross until the end of time. The Mass is the same sacrifice as the sacrifice of the cross."
• Creed of Pope Pius IV: "I profess that the Mass is offered to God a true, proper, and propitiatory sacrifice...and that in the most holy sacrament of the Eucharist there is truly, really, and substantially, the body and blood, together with the soul & divinity of our Lord Jesus Christ."
• The Council of Trent: "The sacrifice (in the Mass) is identical with the sacrifice of the cross...The only difference lies in the manner of offering, which is bloody upon the cross & bloodless on our altars."                                                                   

Transubstantiation:  The Catholic teaching that the wafer & wine of the Eucharist actually become the body & blood of Jesus in substance.  This is rejected by Protestants.

IV. MARY:  She is exalted by many Catholics as an object of veneration which equals worship. Catholics pray to her, and count on her to intercede for them, even for salvation. There is a proposal within some Catholic circles to create a new dogma appointing Mary as "Co-Redemptrix", or Co-Redeemer with Christ. The papal bull The Immaculate Conception is erroneously believed by many to mean that Jesus' birth was miraculous. The doctrine actually teaches that Mary was born sinless, & remained sinless throughout her life - this is opposed to Scripture. The papal bull The Assumption of Mary teaches that God took Mary up to heaven & she did not taste death. These Catholic teachings concerning Mary are rejected by Protestants.  Protestantism teaches from Scripture that while Mary was indeed a vessel "blessed & chosen by God", she was nonetheless a fallen vessel of humanity whom God chose to use.  In Luke 1:47, Mary calls God "her Savior".  For further study on Mary, see:  A Biblical Analysis of the Veneration of Mary.

SOURCES:
Hebrew /Greek Key Study Bible (NAS); Dr. Spiros Zodihates, AMG Publishers: Chattanooga.
Bettenson, Henry, (Ed.) Documents of the Christian Church, 2nd Ed.  Oxford:  Oxford Univ. Press, 1963.
Boettner, Loraine. Roman Catholicism, Phillipsburg: The Presbyterian & Reformed Publishing Co., 1962
Hardon S.J., John A. Pocket Catholic Cateschism New York:  Image Books/Doubleday, 1989
Kistler, Don (Ed.) Sola Scriptura Orlando:  Reformation Trust Publishing, 2009
Latourette, Dr. Kenneth Scott. A History of Christianity: Vol I &II, Peabody: Prince Press, 1975