Exodus 30:10

Once in a year. This refers to the great Day of Atonement, the 10th day of the 7th month, when the high priest was to take the blood and put it on the horns of the altar of incense “and make an atonement for it” (Lev. 16:18, 19). This did not make of it an altar of atonement. It was involved in atonement, however, in cases where the high priest sinned (see Lev. 4:3-12), or when the whole congregation committed iniquity “through ignorance” or did “somewhat against any of the commandments of the Lord” (Lev. 4:13—21). Upon such occasions the high priest touched the blood of the sacrifice to the horns of the altar. In these two instances the altar of incense took the place of the altar of burnt offering, on which was sprinkled the blood of private sin offerings (Lev. 4:22-35). Of all articles of furniture in the tabernacle the altar of incense seems to have been next in importance to the ark and the mercy seat in sacredness. This suggests the great value God places upon prayer (see PP 353).