Numbers 4:13

“And they shall take away the ashes from the altar, and spread a purple cloth thereon.] Having cleared the holy of holies, and the holy place, they were to come forth from thence into the court of the tabernacle, where stood the altar of burnt offering, which is here meant, and on which sacrifices being daily burnt, there were always ashes to be removed; and which at this time was highly necessary to be done, when the tabernacle was taken down, and all belonging to it to be carried away; and though no mention is made of the fire, which was always burning on it, it was doubtless preserved, and care was taken for the carrying it along with the altar, or in a separate vessel from it. Bishop…”

“shall take away the ashes from the altar, &c.--The necessity of removing ashes from the altar plainly implies that sacrifices were offered in the wilderness (compare Exo 18:12; Exo 24:4), though that rebellious race seems frequently to have neglected the duty (Amo 5:25). No mention is made of the sacred fire; but as, by divine command, it was to be kept constantly burning, it must have been transferred to some pan or brazier under the covering, and borne by the appointed carriers.”

“The altar - Hence we may conclude, that they did offer sacrifices at other times, though not so constantly and diligently, as they did in Canaan. Moreover the taking away of the ashes only doth sufficiently imply that the fire was preserved, which as it came down from heaven, Lev 9:24. So it was by God's command to be continually fed, and kept burning, and therefore doubtless was put into some vessel, which might be either fastened to the altar and put within this covering, or carried by some person appointed thereunto. Numbers 4:15”

“The embers of the sacred fire seem to have been removed in the grate, which was carried apart from the brazen altar; both being covered from view by purple cloths. Num 4:6-9, Num 4:11, Num 4:12; Exo 27:3-5, Exo 39:1, Exo 39:41; Lev 6:12, Lev 6:13 Numbers 4:14”

“The altar of burnt-offering was first of all to be cleansed from the ashes; a crimson cloth was then to be covered over it, and the whole of the furniture belonging to it to be placed upon the top; and lastly, the whole was to be covered with a sea-cow skin. The only thing not mentioned is the copper laver ( Exo 30:18), probably because it was carried without any cover at all. The statement in the Septuagint and the Samaritan text, which follows Num 4:14. respecting its covering and conveyance upon a frame, is no doubt a spurious interpolation. Numbers 4:15”