A "falling away" seems to be described in 1 Jn. 2:19: "They went out from us, but they were not of us; for if they had been of us, they would no doubt have continued with us: but they went out, that they might be made manifest that they were not all of us."
"The apostasy" seems to be speaking of born again believers who get caught up in false doctrine, as in 1 Timothy 4:1, which says, "Now the Spirit speaketh expressly, that in the latter times some shall depart from the faith, giving heed to seducing spirits, and doctrines of devils."
"The departure" may very well be referring to the Rapture of the Church (Jn. 14:1-3; 1 Thes. 4:13-18; Rev. 3:10). In this interpretation, the Church, being indwelt by the Holy Spirit, is serving as a restraining force, which is preventing the appearance of the Antichrist (2 Thes. 2:7-8; Rev. 13:1-8;19:19-20).
Based upon the view that the seven churches of Asia (Rev. 2 - 3) represent both, literal churches during the time of the Apostle John's writing, and symbolic representations of historical periods throughout Church History, the Church of the last days will be made up of two kinds of Christians: professing, that is, "the tares," and the possessing, or "the wheat" (Mt. 13:24-30). I believe these two groups are described as co-existing today in the Church of Philadelphia and the Church of Laodicea (Rev. 3:7-22). Notice that the Church of Philadelphia is promised to be removed, that is taken in the Rapture prior to the Tribulation (Jn. 14:1-3; 1 Thes. 4:13-18; Rev. 3:10). The Church of Laodicea, a church in name only, is described as operating with Jesus standing on the outside (Rev. 3:20)!
Jesus was speaking of "the tares" when He said, "Not every one that saith unto Me, Lord, Lord, shall enter into the kingdom of heaven; but he that doeth the will of My Father which is in heaven. (Mt. 7:21). Jesus said that the will of God was for man to believe in Him (Jesus), the One sent by the Father (Jn. 6:29). Believing in Jesus results in being born again by the working of the Holy Spirit (Jn. 3:3-8). For the born again believer, using the title, "Lord," denotes a turning from a self-controlled life, one best described as Godless, to accepting the authority of Jesus Christ. For those who are merely religious, it is nothing more than a form of religious jargon, a blasphemous form of "name dropping."
We only have the right to call Jesus Lord if we allow Him lordship over us!