You may not offer upon it… (Exodus 30:9)
After commanding the kohanim to burn incense on the golden altar, the Torah then rattles off a list of things that may not be burned there: any incense other than the two prescribed daily; burnt offerings; meal offerings; wine libations. In short, aside from the two daily incense services, nothing is to be burned on the golden altar. (Okay, there is one exception. On Yom Kippur, some blood from the bull and goat sacrifices was sprinkled on the golden altar, but that’s it.)
The Sefer HaChinuch is surprisingly elusive as to the underlying rationale for this mitzvah. He says that, if pushed for a reason to this mitzvah, he would say that God commanded us to build the Mishkan (Tabernacle) with certain vessels constructed in a certain way. Together, they comprise a well-oiled machine. (That’s my metaphor, not the Chinuch’s.) It seems to me that to misuse one of the vessels would be like putting diesel fuel in a car that’s not designed for it or, as we learned not to do in shop class, using a chisel instead of a screwdriver to open a can of paint. “Inappropriate use of materials” impedes their ability to get the job done.
The prohibition against burning foreign objects on the golden altar applies to male kohanim when the Temple is in service. (It’s unclear to this author why it shouldn’t apply to everyone. Yes, the kohanim were the ones who were supposed to serve at the altar, but wouldn’t a Levi or a Yisroel burning something on this altar also violate this prohibition?) This mitzvah is discussed in the tractate of Menachos on 50a-b, as well as in Kerisos. It is codified in the Mishneh Torah in the second chapter of Hilchos Klei HaMikdash and it is #82 of the 365 negative mitzvos in the Rambam’s Sefer HaMitzvos.