From the early Church Fathers to now.
1 Patristic · 2 Medieval
“Who hath given testimony to the word of God, and the testimony of Jesus Christ, what things soever he hath seen.”
“Who bore witness to the word of God, and the testimony of Jesus, etc. Lest you doubt the person of John, it is he who bore witness to the eternal Word of God and the same incarnate, as he saw, saying: We have seen his glory, the glory as of the Only Begotten from the Father (John 1).”
“Who hath given testimony to the word of God, and the testimony of Jesus Christ, what things soever he hath seen. John gave testimony then, and now the Church does, whose symbol he was bearing when he saw this Apocalypse. He makes a distinction between the Word and Jesus Christ because of the two substances of Christ — he who gave testimony to both, saying, in the beginning was the Word, [John 1:1] as well as the Word was made flesh. [Ibid. 14] Saw refers to both: for he saw the Word with his spiritual eyes, and with his physical eyes he saw everything that is told about his humanity.”
“Who has given testimony to the word of God In the beginning of his gospel about his eternal Godhead saying, "In the beginning was the Word and the Word was with God and the Word was God (Jn. 1:1)"; that is about to his incarnation, saying, "And the Word was made flesh, etc.(Jn. 1:14)" Therefore, he adds: And the testimony of Jesus Christ, That is, concerning Jesus Christ. he has seen In His way of life, in His miracles, in His death and resurrection, as he clearly shows in the words his Gospel.”
The in-app commentary runs from the Fathers to the early-modern record, then stops — that's where the public-domain sources end, not where the reading does. For the modern reading, follow the sources directly.