Lévitique 6:2

Instruct Aharon and his sons, saying, This is the law of the burnt offering which is brought to make atonement for the thoughts (errors) of the heart: it is a burnt offering, which is made in (the manner of) the burnt offering at Mount Sinai, and abideth upon the place of burning on the altar all the night until the morning: for the fire of the altar shall be burning in it.

It is the burnt-offering [Hebrew: ‘olah] so called because all of it ascends [Hebrew: ‘ olah] up to the Altar. This verse implies that one should not sacrifice the burnt-offering at night, because it must burn on the pyre all night. The word the pyre ends in an extra heh (or perhaps Hebrew contains both a masculine and a feminine form of the word).

the fire of the altar shall burn upon it but not outside of it

TZAV’ (COMMAND) AARON. In the [preceding] section of Vayikra, Scripture stated, Speak unto the children of Israel, for there He gave the command about the bringing of the offerings, and it is upon the Israelites to bring them. But here He states, Command Aaron and his sons, for He now speaks of the rites of the offerings and these are performed by the priests.
Now Rashi wrote: “Command Aaron. The expression ‘command …’ always implies urging [to fulfill the command] at once, and also for future generations. Rabbi Shimon said: Scripture found it especially necessary to urge, in cases where fulfillment of a command involves monetary loss.”], preceded it by the expression, ‘command’ Aaron and his sons, saying: This is the law of the burnt-offering, in order to urge them on to fulfill the commandment. — Ramban, however, argues that even from the burnt-offering the priests do derive a personal benefit, namely, the hide (further, 7:8). Accordingly he will interpret Rabbi Shimon’s statement as referring to another matter, as he explains further on. But the explanation of Rabbi Shimon was not [said] with reference to this command, for here there is no monetary loss involved to the priests to whom this command was given. Indeed, they gain profit and reward from all the offerings,, Verse 9). even the burnt-offering.) [when a Mishnah or a Beraitha cites a number of different authorities, and the first authority is mentioned annonymously, that opinion generally is referred to that of the Tanna Kamma] who said that the expression “command …” is mentioned here because it is a commandment binding at once and also for future generations, while Rabbi Shimon holds that this is not the reason for its use; instead, the reason for the expression “command …” is because in attending to the burnt-offering the priests suffer a monetary loss, and hence they have to be urged on. Ramban, however, argues that even in the case of burnt-offerings the priests incur no monetary loss, since they keep the hides, hence Rabbi Shimon also agrees with the First Sage that the reason for the use of the expression “command …” in this context is because it is a command binding at once and for future generations. Ramban then continues by saying that Rabbi Shimon’s statement has no bearing on our subject of the burnt-offering, but its meaning is as will be explained further on. Rather, the intention of the First Sage [whom Rashi quoted] in …

זאת תורת העולה, this portion now deals in greater detail with the variety of offerings which have been mentioned and discussed in some detail already in Parshat Vayikra.

הוא העולה, that is burned up on the altar during the day, as is clear from 19,6 where reference is made to “the day on which on which you slaughtered,” or in 7,16 ביום הקריבו את זבחו, “on the day he offered his meat offering, etc.”

כל הלילה, the remains are allowed to burn to ash.

ואש המזבח תוקד בו, both by day and by night.

צו את אהרן זאת תורת העולה, after the Torah had informed us about most of the sacrifices and how they were to be offered, the Torah now refers to the specific “Torah” pertaining to each of these voluntary burnt offerings. We pointed out already that different people who feel the need to offer this sacrifice are motivated by quite different considerations. The variety of sacrificial offerings provided for by the Torah corresponds roughly to the variety of human personalities and the considerations motivating their actions. The Torah mentions as a salient feature of the burnt-offering, עולה, that the entire animal is offered on the altar for ריח ניחוח, “sweet smelling fragrance,” although only a small part of it is actually going up in flames. It is this small part which is truly the sacrifice called עולה. Further parts of that sacrifice (animal) [which burned to ash from the heat but did not go up in flames. Ed. ] are deposited אצל המזבח, next to the altar after having turned to ash. Those parts are referred to as דשן, containing a certain degree of moisture which gives the fire a chance to smolder within them. This is meant by the words אשר תאכל אותם האש את העולה, some of it, when completely turned to ash is removed outside the camp while the priest carrying same wears garments of a lower rank. Even though these ashes are just that, ash, the place they are being consigned to cannot be just any dump but must be a site described by the Torah as טהור, ritually pure. [A significant ingredient of this “Torah”, (call it symbolism if you will) of the Olah is the מוקד, the burning center of the altar. We do not find the expression in connection with the other sacrifices. Perhaps this is symbolic of the “rising” of the עולה heavenwards. Ed.]