The Torah tell us that Rachel was beautiful but that Leah had "bleary eyes"? On a deeper level, this describes two personality types—the conventional spiritual beauty of the perfect tzadik and the unconventional spiritual beauty of the struggling penitent. It is the latter who has a special power to take on the spiritual darkness of this world and refine it. One such story is about a young man who wanted more than anything to remain in yeshiva but his Rebbe sent him to drive a tractor.
Based on Likkutei Sichos vol. 35, pp. 152-154.