Jerome

And there will be the light of the moon, like the light of the sun, and the light of the sun will be seven times brighter, like the light of seven days, on the day when the Lord binds up the wounds of his people and heals the bruises inflicted by his blow. LXX: And the light of the moon will be like the light of the sun, and the light of the sun will be seven times brighter, on the day when the Lord heals the brokenness of his people and cures the pain of your wound. …

Commentary on Isaiah ↗

Bede

Moreover, when the day of judgment has been completed and the glory of the future life has become evident with the new heaven and the new earth, then will come to pass what the same prophet announced elsewhere: "The light of the moon will be as the light of the sun, and the light of the sun will be increased sevenfold, like the light of seven days."

On the Gospel of Mark 4:13.24 ↗

Thomas Aquinas

682. Third, the radiance of heaven: and the light of the sun shall be as the light of seven days, that is, as much light in one day as there is now in seven days, as if sevenfold; or as it was in the first week of seven days. The Jews preposterously say that these things are fulfilled literally in the golden age of Jerusalem; but it is better understood as referring to the future glory of the saints, after the renewal of the world; or metaphorically and hyperbolically, it may refer to the state of the people: who heals the broken of …

Commentary on Isaiah ↗