Derasha 583 on Mishpatim 23:20

English: Rava said to Rabbah bar Mari: From where is this saying of the Sages derived: “When we were young, we were like men; now that we have aged, we are like children”? He replied: At first it is written, “Hashem went before them by day in a pillar of cloud, to lead them on the way, and by night in a pillar of fire, to give them light”; and afterward it is written, “Behold, I send an angel before you to guard you on the way.”