Matthew Henry Commentary Leviticus 6:8-13

"And Jehovah spake unto Moses, saying, Command Aaron and his sons, saying, This is the law of the burnt-offering: the burnt-offering shall be on the hearth upon the altar all night unto the morning; and the fire of the altar shall be kept burning thereon. And the priest shall put on his linen garment, and his linen breeches shall he put upon his flesh; and he shall take up the ashes whereto the fire hath consumed the burnt-offering on the altar, and he shall put them beside the altar. And he shall put off his garments, and put on other garments, and carry forth the ashes without the camp unto a clean place. And the fire upon the altar shall be kept burning thereon, it shall not go out; and the priest shall burn wood on it every morning: and he shall lay the burnt-offering in order upon it, and shall burn thereon the fat of the peace-offerings. Fire shall be kept burning upon the altar continually; it shall not go out." — Leviticus 6:8-13 (ASV)

The daily sacrifice of a lamb is chiefly referred to. The priest was to take care of the fire upon the altar. The first fire upon the altar came from heaven (Leviticus 9:24); by keeping that fire continually burning, all their sacrifices might be said to be consumed with the fire from heaven, as a token of God's acceptance.

Thus, the fire of our holy affections, the exercise of our faith and love, of prayer and praise, should be without ceasing.