A few months ago by Chanukah we discussed the apparent stirah between the Rambam's view (as interpreted by the Rogatchover) that the Chashmonaim lit just the ner ma'aravi and the gemara's din that all the neiros are m'akev for the menorah to be complete. There are two dinim at work: 1) a chiyuv to light the menorah, which can be accomplished by lighting even one ner; 2) a chiyuv for the chetftza of the menorah to be lit, which is accomplished only if all the candles are kindled.
Perhaps this explanation sheds light (no pun intended) on Rashi/Ramban on our pasuk. According to Rashi, our parsha is talking about the chiyuv for the cheftza shel menorah to be lit. Therefore, "tamid" must mean consistently, not constantly, as one ner tamid does not a menorah make. Ramban, however, understood the parsha as speaking of the chovas ha'gavra of lighting, which can be fulfilled even by kindling one candle, and therefore he interprets "tamid" to mean constantly.
R' Shimon Sofer uses the symbolism of menorah as representing Torah to derech derush offer another explanation of "tamid." It's not just when learning or sitting in shul that one should feel inspired by Torah, but rather Torah's impact should be felt throughout the day. We need to behave and think at all times, "tamid," like people en-light-ened by the menorah, by Torah. How does that happen? Only if the Torah we study is "shemen zayis zach," pure and unadulterated -- 100% A+ quality of the real thing.
The Chasam Sofer quotes the Hafla'ah who is medayek is the words "shem zayis" - -singular -- "zach." How much oil could one olive produce?! Yet that little bit was enough to keep the menorah lit. We sometimes excuse ourselves from trying to sparking the interest of others in Torah by saying the effort required would be too great and too demanding. The Torah here is telling us that sometimes just a small drop of effort, of Torah, of love, is all it takes.