Comentario sobre Levítico 16:13

על האש UPON THE FIRE which was in the censer.

Which is within [the incense-pan]. [Rashi says this] to preclude explaining that there was another fire “before Adonoy” onto which he put the incense. Therefore he explains that he places the incense “’on the fire’ which is within the incense-pan.” “Before Adonoy” means [that he put the incense on the fire] inside [the Holy of Holies] and not outside like the opinion of the Sadducees.

ונתן את הקטורת, “he will place the incense, etc.” this incense has been mentioned in verse 2 where G-d explained that he will be making an appearance above the lid of the Holy Ark, beyond the dividing curtain. At that point, Aaron, and of course, anyone of lower rank, is not to go there on pain of death unless commanded to do so by G-d. G-d had made clear that no human being while inside a body can ever have a visual image of His essence. In order to make this point quite clear the Torah writes that the cloud of the smoke from the incense will fill that area so that nothing can be seen.