Gospel Beginnings

Et quare Joannes statim in principio Evangelli sui divinitatis ejus monstravit naturam dicens: In principio erat Verbum, et Verbum erat apud Deum? Quoniam Joannes, inter gentes in exsilio constitutus, Graeco sermone Evangelium causa gentium scripsit, quae non cognoscebant si Deus Filium habet, aut quomodo genitum habet: idcirco superfluum erat primum incarnationis ejus mysterium gentibus demonstrarem cum illum ipsi quis esset nescirent: ideo necessarium fuit primum illis ostendere, quia est Filius Dei Deus: deinde in sequentibus, quia carnem suscepit, dicens: Quia Verbum caro factum est, et habitavit in nobis. Matthaeus autem Evangelium Judaeis Hebraico sermone conscripsit, sicut jam diximus supra, ut Judaei legentes aedificarentur in fide. Judaei enim semper cognoscebant, quia est Filius Dei, et quomodo est Filius Dei. Superfluum ergo erat exponere eis divinitatis ejus naturam, quam ipsi optime cognoscebant; necessarium autem fuit mysterium incarnationis ejus ipsis ostendere. Opus Imperfectum in Matthaeum, Homilia Prima Source: Migne PG 56.612-613

And why does John in the beginning of his Gospel show the nature of His Divinity saying, 'In the beginning was the Word and the Word was with God? 1 Because John, who was in exile among the Gentiles, on account of them wrote his Gospel in Greek, for those who did not know if God had a Son, or how He was begotten; therefore it was superfluous that he first show the mystery of the incarnation to the Gentiles when there were those who had no knowledge of Him at all, and thus it was necessary first to show to them that the Son of God is God; then following that, because He took up flesh, to say 'The Word was made flesh and dwelt among us.' 2 Matthew wrote his Gospel in the Hebrew language for the Jews, as we have already said, that in reading it the Jews be edified in the faith. For the Jews always knew that He is the Son of God, and how He is the Son of God. Superfluous for him then it was to explain the nature of His Divinity, which they knew very well, but it was necessary to describe to them the mystery of His incarnation. Opus Imperfectum on Matthew, from The First Homily 1 Jn 1.1 2 Jn 1.14