It shall not be put out The fire coming down from heaven, was to be perpetually preserved, and not suffered to go out, partly that there might be no occasion or temptation to offer strange fire, and partly to teach them whence they were to expect the acceptance of all their sacrifices, even from the divine mercy, through the influence of the Holy Spirit, signified by the fire that came down from heaven, which was a usual token of God's favourable acceptance. Every morning Though the evening also be doubtless intended, yet the morning is only mentioned, because then the altar was cleansed, and the ashes taken away, and a new fire made. Thereon Upon the burnt-offering, which thereby would be sooner consumed, that so a way might be made for other sacrifices.
Related Commentaries of Leviticus 6:12
Leviticus 6:12-13
12 And the fire upon the altar shall be burning in it; it shall not be put out: and the priest shall burn wood on it every morning, and lay the burnt offering in order upon it; and he shall burn thereon the fat of the peace offerings.
13 The fire shall ever be burning upon the altar; it shall never go out.