1 John 2:18

John probably used a different Greek word translated "children" (paidia, also in 1 John 2:12) because it implies a child who learns. His readers needed to learn what he now revealed.

In the drama of human history all of John’s readers, including ourselves, play our part in the last act. Throughout the New Testament the writers regarded the present inter-advent age, after the Incarnation and before the Lord’s return, as the last hour or the last days. This is the final period before the Lord Himself breaks into history again. Then the first stage of the new age will be judgment (the Tribulation) and the second stage blessing. In the second stage Jesus Christ will rule directly over human beings, first in the Millennium and then in the new heavens and the new earth.

The revelation concerning the appearance of the world ruler who will exalt himself against God was familiar to John’s audience (Daniel 11:36-45; 2 Thessalonians 2:3-5; et al.). However even as John wrote, many little antichrists, people who exalt themselves against God, had arisen. John saw this as evidence that the appearance of the Antichrist was not far away. Antichrists are those who oppose Jesus Christ and His teachings, not just people who profess to be the Messiah. [Note: Stott, pp. 104-5; Plummer, p. 107; Barclay, p. 73.]

"Anti ["against"] can mean substitution or opposition, but both ideas are identical in the word antichristos (in N.T. only here, 1 John 2:22; 1 John 4:3; 2 John 1:7)." [Note: Robertson, 6:215.]