One of the vessels associated with the outer, copper altar (upon which animals were offered, as opposed to the inner, golden altar, upon which the incense was offered) are fire-pans (Sh’mos 27:3). Rashi tells us that the fire pans “had a receptacle in order to take [burning] coals from the [outer] altar to carry them onto the inner altar for the incense.” Although his wording can be interpreted in several ways (as we shall see), the bottom line is that the purpose of the fire-pans was to take burning coals from the top of the outer altar to be used to burn the incense on the inner altar. However, when the Torah (Bamidbar 4:14) gives us the list of the vessels of the outer altar to be packed up with that altar for transport (when the nation traveled), which is essentially the same list as in our verse (the only difference being the absence of the pots used to empty the ashes into, likely because it wasn’t packed up like the other vessels, but was in use even during transport — turned upside-down and placed over the fire to protect it and/or to protect the other vessels from it), Rashi tells us that the fire-pans were used “to rake the coals for the ‘lifting of the ashes,” something done each morning at the start of the services of the outer altar (see Vayikra 6:3). Why does Rashi give two different explanations for the same vessel?
Before trying to understand why Rashi changed his explanation of the purpose of the vessel from Sh’mos to Bamidbar, we should try to figure out whether these two explanations are mutually exclusive, or if both can be true. Although this could lead to some very lengthy digressions, suffice it to say that despite some being of the opinion that there were separate fire-pans used for these two activities, one for the “T’rumas HaDeshen” (lifting of the ashes) and one to bring coals from the outer alter to the inner altar, others say that the same fire-pan can be used for both (at least in the Mishkan). In addition, Rashi’s wording (in Sh’mos) can be understood to mean that one fire-pan was used to take coals off the outer altar and bring them to the inner altar, or to mean that the fire-pan mentioned in the verse was only used to remove coals from the outer alter, with the coals being carried to the inner altar on a different fire-pan (see Maskil L’Dovid). If this is what he meant, then even if a separate fire-pan was used for the incense, it could easily have been the same fire-pan used for the T’rumas HaDeshen that was used to remove some coals from the outer altar and transfer them to another fire-pan, which then brought the coals to the inner altar. Either way, though, we would still need to understand why Rashi chose to mention different uses in each location.
As is widely known, Rashi tries to use the simplest, most straightforward way of understanding the subject he is trying to explain (whether it be a verse or a section of the Talmud), which is often based on the context. In Sh’mos, the fire-pans are mentioned last, even though the first two things listed are used to remove ashes from the altar (albeit not as part of the T’rumas HaDeshen, but when the pile of ashes becomes too high). Between those two “ash removal” tools and the fire-pans, two other vessels are mentioned, neither of which is used for ash removal. Since the context of the placement of the fire-pans in this verse indicates that they are not associated with ash removal, Rashi describes its other major use — taking the coals to be used for the incense from the altar. [The placement of the fire-pans away from the other ash removal tool does not preclude it from also being used for the T’rumas HaDeshen; it had to be separated from them because it is a very different type of ash removal, and the fire-pan’s primary use there is to separate the coals before the ashes are removed for the T’rumas HaDeshen. Nevertheless, being separated from any kind of ash removal likely led Rashi to avoid mentioning the fire-pan’s use for the T’rumas HaDeshen.] In Bamidbar, on the other hand, the fire-pans are mentioned first, shortly after the previous verse mentioned removing the ashes from the altar before it’s packed up for transport. [It is still separated from the other ash removal tool included in the list, so that we don’t conflate the two types of ash removal.] In this context, mentioning the fire-pans close to the removal of the ashes allowed Rashi to mention the fire-pans’ association with the T’rumas HaDeshen, which is more closely associated with the outer altar than coals being brought to the inner altar for the burning of the incense.
Although this may explain why Rashi chose each specific use in each specific location, and perhaps why he only mentioned the one use in each rather than both, it only kicks the can further down the road; we now have to try to understand why the Torah put each mention of the fire-pans in a context that led Rashi to explain them this way.
As previously mentioned, there is a discussion regarding whether the same fire-pan was used for both tasks, or if each task had its own designated fire-pan. If there was a separate fire-pan designated only to take the coals brought to the inner altar for the incense, why was it classified as one of the vessels of the outer altar rather than as being a vessel of the inner altar? This is kind of a trick question, though, as there are no vessels listed for the inner altar, so this fire-pan couldn’t be included in a list that doesn’t exist. [Why there is no list of the vessels of the inner altar would lead to another digression, but it is likely tied to the reason this altar was first taught after the priestly garments rather than with the other major vessels of the Mishkan.] Since the fire-pan that takes coals from the outer altar for use on the inner altar has a connection with both altars (even if it wasn’t used for the T’rumas HaDeshen), it had to be included in the list of the outer altar’s vessels. Either way, then, the mention of the fire-pans had to be separated from the ash removal tools, either because some weren’t associated with any aspect of ash removal (as they could only be used to get the coals for the incense), or because none were associated with the type of ash removal that the first two tools listed were used for. In order to avoid taking sides in this discussion (or because he was taking one side over the other), Rashi only mentioned the use of the fire-pans that everyone agreed could involve the inner altar too.
In Bamidbar, although there is also no explicit mention of any vessels of the inner altar, there is a term used that could include those vessels; “and they shall take all of the service vessels used in the holy [sanctuary] and put them in a garment of blue-dyed wool” (4:12). In fact, Rashi understands the vessels referred to in this expression to be precisely the vessels of the inner altar (which is the topic of the previous verse). If the vessels of the inner altar are already included in this verse, and the fire-pan used to bring the coals to the inner altar qualifies as one of those vessels, the fire-pans mentioned with the vessels of the outer altar two verses later can’t include this fire-pan! Therefore, there is no reason for the Torah to separate the fire-pans associated with the outer altar from the ash removal required before the altar is packed up for transport. And Rashi could only mention the use of the fire-pans that are only associated with the outer altar, i.e. the T’rumas HaDeshen.