Little children, it is the last time: and as ye have heard that antichrist shall come, even now are there many antichrists; whereby we know that it is the last time. (1 John 2:18)

Francis Turretin on the Antichrist, already come into the world in the Bishop of Rome:

Since the place or seat of the Antichrist has been discovered as we have just proved, now the Time of his revealing – when he was to occupy that seat – must be examined. This is a point of contention which is not any less bitterly disputed. For the Pontiffs delay the time of his coming all the way up until the end of the world. Just as the Jews contend that Christ is not yet revealed, so those Romanists imagine the Antichrist still to come, appearing and raging only in the distant future, near the culmination of the age. But we, indeed, persist in saying that the Antichrist has already appeared and is clearly visible, and is not, as our opponents insist, someone to be revealed only near the end of the world. Paul disproves this theory, because already in his day Antichrist had begun to increase in power (II Thess. 2:7), when he says the mystery of iniquity doth already work. John corroborates this fact (1 John 2:18), by stating at that time there are many Antichrists in the world. This could not be said unless the foundations of that horrible apostasy had been laid. I, in point of fact, admit that this has been done secretly and in a concealed manner, so that it is not an easy task to note the moment of his birth, because Satan, the architect of this mystery, has gradually – through various forerunners and corruptions of doctrine – spread the foundation of this tyranny.

Therefore, it is called the mystery of iniquity, the opposite of the mystery of godliness, which taught the birth of Christ only through revelation, so that the mystery of his birth was similarly concealed and hidden, not open and disclosed. So, this truth does not refute our premise, (which will be stated later in fuller detail), that the Antichrist’s birth was also to be a mystery, concealed and hidden until revealed in his time. It ought not to seem astonishing if, even as the beginnings of many things lie hidden to our view, in time their growth and development become visible and apparent to us. Such are the seed beds of corruption planted in republics, sciences, languages and similar things, which begin small and concealed. Yet in their progress and development they manifest as quite immense. In like manner is the corrupt Church. When we understand the mystical birth of the Antichrist was kept obscure by divine decree, so as not to be a birth which was to be revealed, but rather one which was to be kept a mystery, until such time as he was decreed to be revealed and encountered, as the son of perdition.

I am a Reformed Presbyterian. I offer all content as my own personal reflections. I am not a licensed minister.