Musar על שבת 238:6

When we read in 31,16: לעשות את השבת, the extra word את suggests that we should add a little from the weekday to the Sabbath, i.e. commence the Sabbath before sunset. The words: לא תבערו אש, "Do not make a fire" in 35,3, also hint at the statement in the Talmud that wherever we find that the Sabbath is also being desecrated, we are liable to find a conflagration (Midrash Hagadol based on Jeremiah 17,27). Observance of the Sabbath on the other hand, will lead to the redemption and the rebuilding of the Holy Temple. G–d will then be as a wall of fire for Zion, as we know from Zachariah 2,9.