Noticing that the territory of Kings Sichon and Og were suited to grazing their large herds and flocks, the tribes of Reuben and Gad asked Moses if they could take possession of these territories and not cross the Jordan River into Canaan. Moses rebuked them for trying to avoid battling the nations then occupying Canaan. The tribes of Reuben and Gad then promised to help the other tribes conquer their territories on the west bank of the Jordan River before settling themselves on its east bank.
Moderating Asceticism
וּמִקְנֶה רַב הָיָה לִבְנֵי רְאוּבֵן וְלִבְנֵי גָד עָצוּם מְאֹד וגו': (במדבר לב:א)
The descendants of Reuben and Gad had an abundance of livestock. Numbers 32:1
These two tribes wanted to live as shepherds because this occupation is conducive to a meditative lifestyle. Moses initially opposed their proposal, since he knew that until the Messianic Era, it is G‑d’s intention that we confront the physical world – and even combat it when necessary – in order to refine it and elevate it. Moses only agreed after stipulating that they first help their brethren conquer the Land of Israel. The experience of confronting the material world would ensure that their subsequent return to shepherding would not be an escape from reality.

Similarly, we should not view the time we are forced to spend in the mundane world, elevating and refining it, as an annoying nuisance. Rather, we should view it firstly as our true Divine mission, and secondly, as the key to ensuring that we study the Torah, pray, and perform G‑d’s commandments with pure and proper intentions.1

FOOTNOTES
1. Reshimot 51; Likutei Sichot, vol. 33, p. 198.