He had, by this unremitting application, become the best grammarian and critic of his time. He had long seen, as I have said, that the Vulgate was obscure and full of inaccuracies; and therefore it was determined to publish the Christian Scriptures in their original tongue, along with a translation of them into Latin from the Greek. He was the first to undertake this work. He consulted all the manuscripts which he could discover; he carefully read the works of the Fathers and the Greek Commentators, marking down from them the various readings; that he might give the Greek text as correctly as possible. The Latin translation is printed side by side with it, with Annotations. We may mention as remarkable proof of his sagacity and diligence, that he was the first to discover that the words in 1 John [5] v. 7,8, "In heaven, the Father, the Word, and the Holy Ghost, and these three are one. And there are three that bear witness in earth," are not genuine, and that the passage should stand thus: "For there are three that bear record, the Spirit, and the water, and the blood, and these three agree in one." Erasmus had, however, pledged himself in his controversy with Lee, to insert the words if they existed in one Greek manuscript. A Codex Britannicus, written probably under Lee's direction, was at length found which contained them. Then Erasmus, for the sake of peace, published the words in the third edition. His translations from Greek are wanting in accuracy, because he lived in an age in which there were no dictionaries, and no good editions of the Greek authors. We are quite willing, too, to admit that as we might have expected, the Greek text, having been brought out when the study of Greek had only just commenced in Europe, is very imperfect, and will not stand the test of modern criticism. Still we may venture to affirm that his notes contain many exact philological remarks, founded on a knowledge of the Greek language, of the style of the Scriptures, and of the doctrine of the Fathers, and that though he has been surpassed by many men inferior to him in ability and industry, who lived at a time when critical knowledge was very generally cultivated, yet he must have the merit given him of having been the pioneer in that work of criticism which has shed a bright light on many parts of the records of heavenly truth.

The life and character of Erasmus (pg 173-175) - A.R. Pennington