The answer to this question is not explicitly mentioned in the passage. In attempting to come to an understanding, it is important to recall the meaning of the burnt offering from Leviticus 1:1–17. The burnt offering was presented in order to make atonement and find acceptance before the presence of the Lord. By keeping the fire burning, the priests communicated that atonement was always available for the people of God. In other words, the perpetual fire signified that access to God was always ready and available.
9 “Command Aaron and his sons, saying, This is the law of the burnt offering. The burnt offering shall be on the hearth on the altar all night until the morning, and the fire of the altar shall be kept burning on it.