Gregory the Great — as excerpted in the Catena Aurea on Luke 21:28-33

“(ut sup.) That the world ought to be trampled upon and despised, He proves by a wise comparison, adding, Behold the fig tree and all the trees, when they now put forth fruit, ye know that summer is near. As if He says, As from the fruit of the tree the summer is perceived to be near, so from the fall of the world the kingdom of God is known to be at hand. Hereby is it manifested that the world’s fall is our fruit. For hereunto it puts forth buds, that whomsoever it has fostered in the bud it may consume in slaughter. But well is the kingdom of God compared to summer; for then the clouds of our sorrow flee away, and the days of life brighten up under the clear light of the Eternal Sun.”