1 But the Spirit explicitly says that in later times some will fall away from the faith, paying attention to deceitful spirits and doctrines of demons, 1 Timothy 4:1 (NASB)
According to the words of our Lord Jesus Christ in John 15 the mark of Christian authenticity is abiding or remaining in Him. This is not simply a continual profession of faith, but a remaining faithful to Christ in our orthodox Christian faith. According to Paul, this falling away is a two-fold action of departing from the faith and giving heed to seducing spirits, and doctrines of devils. The Apostle John called the Christian leaders who do this antichrists.
18 Children, it is the last hour; and just as you heard that antichrist is coming, even now many antichrists have appeared; from this we know that it is the last hour. 19 They went out from us, but they were not really of us; for if they had been of us, they would have remained with us; but they went out, so that it would be shown that they all are not of us. 1 John 2:18-19 (NASB)
John was describing his own time. In the 1st Century Church there were already “many antichrists” and this was a sign that “it is the last time.” In v18 the word “last” translates the Greek adjective ἐσχάτη (eschatē) the nominative singular feminine case of ἔσχατος (eschatos). When this word is used in reference to time it refers to “the last” generally that which concludes anything. Biblically, it refers to the time when the development of God’s plan of salvation shall come to a close as well as to the time of the final and decisive judgment. The word “hour” in v18 is translated as “time” in the KJV. It is translates the Greek noun ὥρα (hōra). Its literal translation is “hour.” However, in the New Testament it is used to mean many different time oriented things. In this passage, though, John is making the case that since “antichrists” have already come in the 1st Century then the Church is the “last days,” which refers to the time between Christ’s first and seconding coming.