Gregory the Great — as excerpted in the Catena Aurea on Luke 19:41-44

“(Hom. 39. in Ev.) The merciful Redeemer wept then over the fall of the false city, which that city itself knew not was about to come upon it. As it is added, saying, If thou hadst known, even thou (we may here understand) wouldest weep. Thou who now rejoicest, for thou knowest not what is at hand. It follows, at least in this thy day. For when she gave herself up to carnal pleasures, she had the things which in her day might be her peace. But why she had present goods for her peace, is explained by what follows, But now they are hidden from thy eyes. For if the eyes of her heart had not been hidden from the future evils which were hanging over her, she would not have been joyful in the prosperity of the present. Therefore He shortly added the punishment which was near at hand, saying, For the days shall come upon thee.”