St. John, in his old age, was much troubled by false teachers, who had begun to corrupt the Gospel. These persons are called "heretics", and their doctrines are called "heresy" from a Greek word which means "to choose", because they chose to follow their own fancies, instead of receiving the Gospel as the Apostles and the Church taught it. Simon the sorcerer, who is mentioned in the eighth chapter of the Acts, is counted as the first heretic, and even in the time of the Apostles a number of others arose, such as Hymenaeus, Philetus, and Alexander, who are mentioned by St. Paul (1 Tim. i. 19f; 2 Tim. ii. 17f). These earliest heretics were mostly of the kind called Gnostics,-- a word which means that they pretended to be more knowing than ordinary Christians, and perhaps St. Paul may have meant them especially when he warned Timothy against "science" (or knowledge) "falsely so called" (1 Tim. vi. 20). Their doctrines were a strange mixture of Jewish and heathen notions with Christianity; and it is curious that some of the very strangest of their opinions have been brought up again from time to time by people who fancied that they had found out something new, while they had only fallen into old errors, which had been condemned by the Church hundreds of years before.
St. John lived to about the age of a hundred. He was at last so weak that he could not walk into the church; so he was carried in, and used to say continually to his people, "Little children, love one another." Some of them, after a time, began to be tired of hearing this, and asked him why he repeated the words so often, and said nothing else to them. The Apostle answered, "Because it is the Lord's commandment, and if this be done it is enough."
Adapted from Sketches of Church History (public domain) by Reverend J.C. Rbertson. First Published in 1904