וְעָשִׂ֥יתָ מִזְבֵּ֖חַ מִקְטַ֣ר קְטֹ֑רֶת עֲצֵ֥י שִׁטִּ֖ים תַּעֲשֶׂ֥ה אֹתֽוֹ׃
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Rashi
מקטר קטרת FOR THE BURNING OF INCENSE — to raise smoke (קיטור) on it, viz., the smoke of incense.
Ramban
AND THOU SHALT MAKE AN ALTAR TO BURN INCENSE UPON. Now the altar of incense being one of the articles in the inner part of the Sanctuary, it should have been mentioned with the table and the candelabrum together with which it was placed, as indeed they are mentioned at the actual construction in the section of Vayakheil.232Further, 37:25 — next to the making of the candelabrum. But the reason for mentioning it here after the Tabernacle and all its vessels and the sacrifices [for the seven days of consecration], is because of what He said at the completion of them all, and the Tent shall be sanctified by My Glory;233Above, 29:43. and I will dwell among the children of Israel.234Ibid., Verse 45. Therefore He now said that they will yet be obliged to make an altar for the burning of incense — to burn it for the glory of G-d. This was a secret which was transmitted to Moses our Teacher,235Shabbath 89a. that the incense checks the plague.236Numbers 17:11-13. For the incense is of the attribute of justice, as it is said, they shall put incense ‘b’apecha’,237Deuteronomy 33:10. It is generally translated: “before Thee,” but Ramban suggests that b’apecha is of the root aph (anger). which is of the root v’charah api (My wrath shall wax hot).238Above, 22:23. It is for this reason that He said of strange incense, and before all the people I will be glorified,239Leviticus 10:3. meaning that they will know My glory, for He will not pardon your transgression.240Above, 23:21. For this reason too He said here [of the altar of incense], And thou shalt put it before the veil that is by the ark of the Testimony, before the ark-cover that is over the Testimony, where I will meet with thee.241Verse 6. For why is it necessary to speak at length of all these matters, and why did He not say briefly, “and thou shalt put it before the ark of the Testimony in the Tent of Meeting,” as He said in the section of Vayakheil?242It is found in the section of Pekudei (further, 40:5). But the extended form of the verse here indicates the purport [of the altar of incense].
Rashbam
FOR BURNING INCENSE. But not for a burnt offering, well-being offerings, grain offerings, or libations.