"of whom you have heard that he is coming," refers to the person of the Antichrist, NOT in existence at that time but reserved for the future.
"and now is already in the world." refers to the spirit of the Antichrist which is the spirit of Apostasy which is the spirit of the Devil, the wicked one.
Heresies that divide and apostasy to unite a fragmented Church is the instigation and Diabolic plan of the Devil a murderer and liar from the beginning.
The faith is transmitted by the witness of those who hold directly to the Head of His Church, His body, which is Jesus Christ and no other, to true parádosis which is true tradition and not traditionalism. The Head and body together are His Church and no other.