Horav S.R. Hirsch, z.l., notes that this is the first time that the name irah, straight and morally upright, is mentioned. This word designates and defines Bnei Yisrael according to the ideal of its moral mandate. This implies that Bnei Yisrael should be “yashar,” straight, never deviating from the correct path of service to the Almighty.
Hashem desires that we ascend to the summit of achievement in the dual heights of human aims; the highest of material good fortune and spiritual/moral perfection. We are to serve as an illuminating example to the secular world that a life devoted entirely to spiritual and moral perfection by no means demands a renunciation of earthly happiness. On the contrary, a life devoted to Torah and mitzvos is in harmony with material wealth and enjoyment. Materialism can be sanctified by its dedication to moral deeds and spiritual developments.
Bnei Yisrael, however, have a problem relating to abundance. The pasuk says, “As often as you waxed fat, you became obese, and (you) became overcome by fat.” Horav Hirsch views this verse as being parenthetical to the beginning of the pasuk. It contains the essence of the historical perspective of Klal Yisrael. In suffering we thrive. In times of good fortune, we fall prey to the yetzer hora, evil inclination.
The history of Klal Yisrael has reflected that when we receive more “fat” to be transformed into energy and good works, we employ it instead to become slaves to this corpulence. We have not used the abundance for the common good. We have not been able to master our riches and good fortune for Torah and mitzvos. We should learn that whatever good fortune we receive, is granted for a purpose. It serves as an opportunity for greater moral and spiritual achievement. With this idea in mind, we pray to Hashem for abundance, so that we can use it to attain greater spiritual accomplishments.
