Jamieson, Fausset and Brown on Leviticus 24:5-9

5-9. take fine flour, and bake twelve cakes--for the showbread, as previously appointed (Ex 25:30). Those cakes were baked by the Levites, the flour being furnished by the people (1Ch 9:32; 23:29), oil, wine, and salt being the other ingredients (Le 2:13).

two tenth deals--that is, of an ephah--thirteen and a half pounds weight each; and on each row or pile of cakes some frankincense was strewed, which, being burnt, led to the showbread being called "an offering made by fire." Every Sabbath a fresh supply was furnished; hot loaves were placed on the altar instead of the stale ones, which, having lain a week, were removed, and eaten only by the priests, except in cases of necessity (1Sa 21:3-6; also Lu 6:3, 4).