Hunger is an outward difficulty of fasting. Its goodness is not explained merely by saying that hunger is difficult.
Fasting restrains the lower self and its desires1. Desire is the intermediary: without it, this restraint would not be needed. The comparison with angels makes that point; they do not have these desires, so fasting has no such distinct merit for them.
Allah created human desire; the person did not create it by choosing an action. This intermediary is therefore treated as absent, and fasting is attached to intrinsic goodness.
1. Desires of the lower self: inclinations that need restraint; the term here is not limited to sexual desire.
- Fasting: Understanding the Restraint