Parashas Eikev · Passuk 8:16
who fed you in the wilderness with manna, which your ancestors had never known, in order to test you by hardships only to benefit you in the end—
Torah Temimah points to Yoma 74b.
TT lemma: למען ענתך.
English: What is “in order to afflict you”? R’ Ammi and R’ Assi: one said, one who has bread in his basket is not like one who has no bread in his basket; the other said, one who sees and eats is not like one who does not see and eat. The Gemara concludes that this is a hint concerning blind people who eat but are not satisfied.
Custom (affliction of the manna; hint for Shabbos lights)
The manna’s daily uncertainty and lack of visible variety are forms of affliction; seeing one’s food is part of oneg Shabbos.