Midrash su Esodo 30:1

And thou shalt make an altar to burn incense (Exod. 30:1). What do the letters in the word ketoret (“incense”) stand for? The kuf stands for kedushah (“sanctification”), tet for taharah (“purity”), resh for rahamim (“mercy”), and ta for tikvah (“hope”). A cubit shall be the length thereof, and a cubit the breadth thereof; and two cubits shall be the height thereof (ibid.). What was the purpose of this altar? After they committed the act of erecting the golden calf, the Holy One, blessed be He, complied with his (Moses’) request, as is said: And the Lord repented of the evil (ibid., v. 14). Whereupon Moses said: Master of the Universe, You have already agreed with me (to forgive them), but who will make known to those who come unto the world that You are reconciled with Israel? He replied: Let them make Me a Sanctuary, that I may dwell among them (Exod. 25:8), and let them offer sacrifices within it, and I will accept their lamb.

And thou shalt make an altar to burn incense upon (Exod. 30:1). Scripture states elsewhere in allusion to this verse: Ointment and perfume rejoice the heart (Prov. 27:9). This verse refers to the Holy One, blessed be He, and to Israel. How is that? When the high priest was officiating on the Day of Atonement, he would place the incense in a pan and bring it into the innermost part of the Holy of Holies, as it is written: And he shall take a censer full of coals of fire from off the altar. What else is written there? Ye shall put the incense upon the fire before the Lord, that the cloud of the incense may cover the ark cover (Lev. 16:12–13). What is the meaning of may cover? It is an expression that indicates forgiveness, as in the verse Thou hast covered up all their sins (Ps. 85:3). Whenever the cloud of incense ascended and spiraled upward, like a cluster of grapes, on the Day of Atonement, he knew that Israel’s sins were forgiven, as it is said: My beloved is unto me as a cluster of henna in the vineyards of En-gedi (Song 1:14). If the smoke of the incense resembled a cluster and rose straight upward, he knew that Israel was forgiven and his service was acceptable, but if the smoke of the incense did not cover the ark-cover he knew that he would die, as it is said: That the cloud of the incense may cover the ark-cover that is upon the testimony, that he die not (Lev. 16:13). Consequently, the high priest and all Israel trembled from the moment the high priest entered the innermost Sanctuary until he withdrew in peace. When he departed from the Sanctuary a great rejoicing took place among the Israelites, since it meant that it (the offering) had been received favorably, as it is said: Ointment and incense rejoice the heart (Prov. 27:9).