This was explained in Savatthi. Standing at one side a certain Devatā addressed the Bhagavā in verses thus:
“Dwelling in the forest and living the life of saints, a holy life,
Living only on one meal, but how can their facial features be so shining?”
“They do not worry about the past, they do not crave for the future.
In the present moment they do dwell, that is why their facial features are so shining.
Craving for the future, worrying about the past,
Thus the foolish people wither away like the green weed being cut off.”