John Wesley on John 1:7

The same came for (that is, in order to give) a testimony - The evangelist, with the most strong and tender affection, interweaves his own testimony with that of John, by noble digressions, wherein he explains the office of the Baptist; partly premises and partly subjoins a farther explication to his short sentences. What St. Matthew, Mark, and Luke term the Gospel, in respect of the promise going before, St. John usually terms the testimony, intimating the certain knowledge of the relator; to testify of the light - Of Christ.