Shraga Dovid Homnick: Chassidus explains that oil represents tremendous wisdom, an association which is sourced in the Gemara, yet we’re told that Asher’s "feet," the lowest and lowliest part of the body, far beneath the mind and heart and only capable of action, are to be serviced with oil. Asher’s "feet" must therefore have been of such a lofty stature to be worthy of such treatment. Furthermore, Moshiach’s legs are described as "standing atop the mount of olives," the mountain being the source of the olives which are in turn the source of oil.
The tribe of Asher belonged to Dan’s camp, along with Naftali, last among the Jews in the desert, yet the camp of Dan is described as collecting and returning the lost objects of the Jews in front of them, resulting in everyone ultimately depending on them. Retrieving what might otherwise be lost, occurs through serving Hashem selflessly, and is what Dan’s camp represents. And among the tribes comprising the camp of Dan, Asher is at the center, the focal point, and therefore the greatest personification of simply following orders out of kabalas ol, eliminating all questions.
When coupled with understanding and emotion, Asher’s "foot" is thus very great indeed, and is deserving of being bathed in oil, and its superiority will become even more apparent when Moshiach comes. In the dispute whether study or action is greater, we currently follow the former view, but the advantage of action will be revealed in the messianic era, and thus Moshiach’s "feet" will be elevated above the "mount of olives."