What is the purpose of the shammash candle on a hanukkiyah?

The shammash (Hebrew for "servant") is the ninth light on the hanukkiyah, the nine-branched candelabra used during the festival of Hanukkah.12

Its primary purpose is to serve as the source of fire used to kindle the other eight candles during the nightly ritual. Because the shammash is considered a "servant" light, its holder is typically offset or positioned higher than the other eight receptacles. During the ceremony, the shammash is lit first, and while holding it, the individual recites the required blessings before using its flame to light the remaining candles.324