The “falling away” described by Paul in our King’s James version of the Bible has an original Greek meaning that is quite different from the gradual, natural drifting into apostasy that we usually interpret the phrase to mean. The falling away in 2 Thessalonians 2:3 comes from the Greek word apostasia, which is also where we get our English word apostasy from. It is constructed from two Greek roots: the verb histemi, “to stand,” and the preposition apo, “away from.”
The word means “rebellion,” “mutiny,” “revolt,” or “revolution,” and is quite a bit stronger than we normally think. And while the great apostasy did happen gradually, people certainly did rise up against early Christianity and seek to replace its leaders and put to silence its doctrines (as in a mutiny or revolution). There was an apostasy, and for most of the world, it still continues today. (see also Acts 20:29-31, 2 Timothy 4:2-3, 2 Peter 2:1-3, Revelation 13:1-9)