Oecumenius

"And we declare to you eternal life, which was with the Father and was revealed to us." "And we declare to you the life." Therefore, what we have seen, we also declare to you, John says. What is that? That he who is eternal life has been revealed to us, and we have become witnesses of him both before his crucifixion and after his resurrection. For he was indeed nailed to the cross in the flesh, and in that same flesh he rose again.

Commentary on 1 John ↗

Clement of Alexandria

"The life was manifested." For in the Gospel he thus speaks: "And what was made, in Him was life, and the life was the light of men." "And we show unto you that eternal life, which was with the Father, and was manifested unto you." He signifies by the appellation of Father, that the Son also existed always, without beginning.

From the Latin Translation of Cassiodorus ↗

Augustine of Hippo

"The Life was manifested." Christ therefore is "the word of life." And whereby manifested? For it was "from the beginning," only not manifested to men: but it was manifested to angels, who saw it and fed on it as their bread. But what saith the Scripture? "Man did eat angels' bread." Well then "the Life was manifested" in the flesh; because it exhibited in manifestation, that that which can be seen by the heart only, should be seen by the eyes also, that it might heal the hearts. …

Ten Homilies on 1 John 1 ↗

Bede

And the life was manifested, etc. He refers to that life which speaks in the Gospel: "I am the resurrection and the life" (John 11); which was manifested through divine miracles declared in the flesh, and the disciples present saw what they would testify to posterity with undoubted truth, when performing signs, as John himself wrote, He manifested His glory, and His disciples believed in Him (John 2). …

Commentary on the Catholic Epistles ↗