Augustine of Hippo

Before the Lord's resurrection there was rest for the departed but resurrection for none: "Rising from the dead he dies no more, death has no more dominion over him." But after such resurrection had taken place in the Lord's body, so that the head of the church might foreshadow what the body of the church hopes for at the end, then the Lord's day—that is the eighth, which is also the first—began to be observed.

Letter 55 ↗

Ambrose of Milan

The Old Testament too knew this number eight which in Latin we call the Octave, for the preacher says, give a portion to seven and also to eight. The number seven belongs to the Old Testament, the number eight to the New, for then Christ rose, and the day of new salvation shone upon all. This is the day whereof the Prophet says, This is the day which the Lord hath made, let us rejoice and be glad in it.

Letter XLIV, To Horontianus ↗

Jerome

"Give a portion to seven, and also to eight; for you do not know what evil shall be upon the earth. "And in Ezekiel there are found seven or eight steps leading up to the temple. [Ez. 40, 26.31.] And after the 'ethical' Psalm, that is one hundred and eighteen, all the psalms are of fifteen steps by which we are first taught the law, and when the seventh is finished, we then climb to the Gospel through the 'eight steps' [Ier. 'ogdoadem']. …

Commentary on Ecclesiastes ↗