One flame of the Menorah, the "western" lamp, burned perpetually. This candle was never extinguished, for the other flames were kindled from its fire. Concerning this flame the verse states, "raise up a constantly-burning lamp" (Lev. 24:2-3). This is the second flame from the end on the eastern side. It is related that until the death of the High Priest Simeon the Just, this flame burned constantly in miraculous fashion, which demonstrated to the world that the Divine Presence dwelled amongst Israel (Baraitha, BT Shabbat 22,2): "Rava said, what is meant by the words (Lev. ibid.) outside the curtain of testimony?' The western candle is the testimony, for it was filled with the same amount of oil as the others, but is not extinguished."
If the priest finds that the two eastern lamps have gone out, he prepares them for rekindling and lights them from the other flames. And if he should ever find that all the flames have been extinguished, he re-lights these two from the fire atop the altar, and then kindles the remaining five.
Before leaving the Sanctuary, he leaves the basket on the second step before the menorah, and then departs.