Deuteronomy 32:15

Jeshurun, meaning "the upright," is a poetical name for Israel carried over from her earlier uprightness, before she took for granted the physical and spiritual blessings that God provided. The metaphor Moses uses derives from a pampered animal that, instead of being tame and gentle, becomes mischievous and vicious as a result of good living and spoiled treatment. Israel did this in various acts of rebellion, murmuring, and idolatrous apostasy.

Martin G. Collins
Gluttony: A Lack of Self-Control (Part Two)