Apostasy is defined as a total desertion of or departure from one’s religion, principles, party, cause.” [1. Definition of Apostasy..] In Christian circles, it carries an even stronger connotation of not being a true believer. So what apostasy means is to fall away from the truth. Therefore, an apostate is someone who has once believed and then rejected the truth of God. Apostasy is a rebellion against God because it is a rebellion against truth and falling away from the truth we are given in Gods Word. We have been warned in prophecy that this would happen in the church, and it did happen.
2 Thessalonians 2:4
Who opposeth and exalteth himself above all that is called God, or that is worshipped; so that he as God sitteth in the temple of God, shewing himself that he is God.
If there is indeed an apostasy occurring in the church, how would we know it unless we first examined the Bible closely and then compared it. But what if the church took away and forbid Gods Word as happened. So how was this able to get in and bring such great apostasy into what Christ and the Apostles brought up with such care. It was through subtle and secret changes, done with evil discipline to hide the apostasy that they brought in slowly, so few would notice.
I was doing a study on the Greeks and how they picked up and passed on to the Romans the ancient Babylonian sun gods and system of worship, when I came across a interesting sermon that really hit the issue of the apostasy in the church dead center.
'...Pope is a shortened title for Pontifex Maximus. In Greek it means father. The Pontifex Maximus (meaning king of sacrifices or servant to the triads, as well as the "greatest bridge-maker between the gods and men") was the high priest of the College of Pontiffs (Collegium Pontificum) in ancient Rome. It's a pagan title that was incorporated from the Etruscan-Latin polytheistic culture (700 BC) who lived before the Romans. These early people (just like the Romans) had built great temples to the gods and goddess of the day. They also had a pagan triad. Eventually the Etruscans were conquered by Rome.
The title Pontifex Maximus (Pope) is mentioned numerous times by the early Catholic Church fathers (especially by Tertullian), but it was not applied to a Catholic bishop until much later on. The early Catholics said that the Pontifex Maximus was the "King of Heathendom," the evil high priest of the pagan mystery religion of Rome. This post was the most important position in the ancient Roman religion. A distinctly religious office under the early Roman Republic, it gradually became politicized until, beginning with Augustus, it was subsumed into the Imperial office. It's last use with reference to the emperors is in inscriptions of Gratian (reigned 375-383). He was then urged by the Catholic bishops to renounce the cultic Roman title, and instead grant it to their exalted leading bishop over Rome.
Pontifex Maximus is a name that's being used by the Roman Catholic Church clergy today. Though it may be abbreviated into Pope or Papa, yet it's clearly a title incorporated directly from paganism. Interesting to note that the all the pagan pontiffs or popes held that office for life. Exactly like the Catholics Popes. And their cult members met and elected a successor, who after his election became the next Pope or Pontifex Maximus (Dionys. II.22, 73). Just like the election held by the Catholic Church cardinals to choose a new Pope. The Pontifex Maximus was the guardian of the Vestal virgins. The Roman Catholic Church has simply named them Nuns instead. Many historians agree that the idea for the powers of the pope with the College of Cardinals came from the Pagan College of Pontiffs with its Sovereign Pontiff which had no doubt been in Rome from the earliest times, and must have been framed on the order of the original Council of Pontiffs at Babylon. It's also obvious to any historian that while the Catholics have called themselves Christians, they more closely resemble the ancient pagans both in customs and names. Pope Gregory I (601 AD) said in so many words literally, "We must compromise with the pagans in order to further Christianity."...'
http://www.upublish.info/Article/The-Pope--Pontifex-Maximus-/693298
By the time of Emperor Constantine, the Christian religion received imperial sanction and the bishop of Rome became more than just another bishop, and brought in a system of worship from another origin than Christianity, in a apostasy that prophecy foretold.
Catholicism is Paganism.