"HaShem spoke to Moshe saying: Command the Children of Israel and say to them: My sacrifice, My food for My burnt-offerings, My satisfying aroma - you will be scrupulous to sacrifice to Me in its correct time. And you shall say to them: This is the burnt-offering that you shall sacrifice to HaShem: male yearling lambs, perfect, two every day, as a continual elevation-sacrifice." (Numbers 28:1-3)
This sequence of sacrificial commandments appears to be out of context. It interrupts the natural flow of the narrative; it is interspersed in the midst of a succession of events that are intimately connected. Back in parashat Chukat (Numbers 20), we arrived in the wilderness of Zin at the beginning of the fortieth year of the Exodus. Then, 
Why does the Torah suddenly insert the laws of daily sacrifices?
in close succession: Miriam died; Moshe brought forth water from the rock; we bypassed Edom and came to Mount Hor, where Aaron died; we were attacked by the Canaanite king of Arad and defeated him; we continued to Oboth on the border of Moab (east of the River Jordan); we were attacked by Sihon and his Amorite nation and defeated them, as we did with Og, king of Bashan; we reached the plains of Moab, where Balak, king of Moab, joined forces with Midian to hire Balaam, the Aramean prophet, to curse us; Moab sent their daughters to seduce our men and thereby caused disaster among us - 24,000 Jews died in the resulting plague; Pinchas arose and publicly wrought vengeance on the Jew and the Moabitess who publicly flaunted their debauchery; Moshe and Elazar took a census of the Jews; HaShem commanded Moshe to publicly nominate Joshua as his successor; and Moshe, at HaShem's command, mustered an army to take revenge against the Midianites.
This is a series of connected events, which span somewhat less than one year. Why does the Torah suddenly insert the laws of daily sacrifices, and Shabbat, Rosh Chodesh and festival sacrifices immediately after appointing Joshua as next national leader?
Commentators have offered different explanations. The Ramban (Italy, Spain and Israel; 1195-c.1270) explains:
"After telling them to divide up the Land of Israel , He commanded them to complete the laws of sacrifices which they would do in the Land, because in the desert they did not offer the Mussaf-sacrifices, as I mentioned in parashat Emor . And similarly, they were not obligated to bring the libation-offerings in the desert, as I explained in parashat Sh'lach Lecha . But now, those who would come into the Land would be obligated in all these sacrifices there - the daily offerings, the Mussaf-sacrifices, the Mincha-sacrifices, and the libation offerings." (commentary on Numbers 28:2)
The Ohr HaChayim(Rabbi Chayim ben Attar; Morocco and Jerusalem; 1696-1743) has a very different approach:
"We have to understand why the Torah put the section of sacrifices here, after Joshua's appointment, and not in its appropriate place with the other sacrifices that were commanded in parashat Emor ; after all, you have to agree that this mitzvah applied as soon as the Mishkan [Tabernacle] was erected [less than a year after leaving Egypt; Exodus 40], whereas Joshua was appointed in the fortieth year."
And the Ohr HaChayim proceeds to give two different explanations:
"Maybe this comes to say that Joshua was forbidden to offer daily sacrifices or Mussaf [additional festival] sacrifices of his own invention, since the communal obligation devolved upon him, too.... And this is why this mitzvah appears immediately after Joshua's appointment: [God] commanded him [to offer] the sacrifices as his communal obligation, as He said, 'Command the Children of Israel...' - thus saying that the daily sacrifices are always communal.... And I have also seen another explanation that the rabbis give [Yalkut Shimoni, Pinchas 776]: 'This is because Israel said: Previously, we were travelling and we were offering daily sacrifices; now that the travellings have ceased, the daily offerings likewise cease. God said to Moshe: Say to them that the daily sacrifices will still continue.'"
These are three very different explanations as to why God decided to insert this series of sacrificial commandments at this juncture. I would like to offer another possible perspective, which I preface with another quote from the Ohr HaChayim:
"Know that permission is given us to explain the meaning of Scripture through our own studying, in ways which satisfy the intellect, even if the earlier Torah authorities explained it in other ways, because 'the Torah has seventy facets' (Numbers Rabbah 13:16). We are forbidden to disagree with the earlier authorities only in cases which change and affect practical halachah. Indeed, you find that the Amoraim [the later generations of Talmudic sages] have no authority to disagree with the Tanaim [the earlier generations of Talmudic sages] in halachic matters, but in commenting on Scripture and explaining its meaning, we often find that they give differing explanations." (Commentary on Genesis 1:1)
And so, with this permission granted, I offer the following observation.
After the giving of the Torah, we committed various sins in the desert. And each time, the Torah's narrative of the sin is followed by mitzvot of sacrifices. The first and most striking example is the sin of the golden calf (Exodus 32), as a result of which some 3,000 Jews were killed by the Levites (32:26-28), as well as an unknown number who died by plague (32:35). Although the Ramban (ibid.) questions whether anyone at all died in this plague, the Midrash (Numbers Rabbah 9:49) understands that there were deaths, as does Rashi (commentary to 32:20).
And immediately following this most heinous of sins, Moshe began to give the nation the commandment to build the Mishkan, the prerequisite for bringing sacrifices (Exodus 35:4 onwards); and sacrifices are the next theme, which take up most of the Book of Leviticus. Indeed, to strengthen this point, Rashi (commentary to Exodus 31:18) says that even the commandments of sacrifices which the Torah records before the sin of the golden calf (25:1 onwards) were actually given after the sin, but that the Torah does not always follow strict chronological order.
The next major sin that the entire nation committed was the sin of the spies, in parashat Sh'lach Lecha (Numbers 13:1-14:45), when they committed the horrendous sin of rejecting the Land of Israel. As a result, God ordained that the entire generation would die in the desert, never seeing the good land that they had spurned. And immediately afterwards, God continued by giving Moshe commandments of sacrifices (Chapter 15).
We next encounter the rebellion of Korach and his followers (Chapters 16-17), as a result of which 14,700 Jews died in a plague (17:14). And immediately afterwards God recapitulated to Aaron, in brief, his and his descendants' duties to officiate in the Mishkan and, afterwards, in the Holy Temple (Chapter 18). This mention of the sacrificial order seems out of context here - unless it was inserted deliberately as a postscript to the punishment
And in last week's parasha, we encountered the nation's mass sin of debauchery with the Midianite women, as a result of which 24,000 Jews died in a plague (25:9). And in the immediate aftermath God completed commanding the sacrificial sequence.
The inference seems to be clear. After every major sin that we ever committed, God inflicted a punishment - many Jews died, we were delayed in our return to our homeland, we were condemned to terrible suffering. But immediately following each and every punishment, God always continued by giving the mitzvot of sacrifices, with the concomitant comfort that repentance is always available, forgiveness is eternally possible.
This is like a father who hits his son when he misbehaves; and as soon as the son cries, the father lovingly 
Following each and every punishment, God always continued by giving the mitzvot of sacrifices.
cradles his son in his arms, comforts him, wipes away his tears, and explains that his chastisement comes out of love, that he wants only to correct his son's behaviour so that he will follow the right path. Every time God chastises us, He then cradles us lovingly in His arms, showing us that He wants no more than for us to repent and choose the right path.
We have just entered the Three Weeks - the period that reverberates through our history as a time of sin and punishment, from the sin of the golden calf and the sin of the spies, to the disasters of the destruction of two Holy Temples, the fall of Beitar, the expulsion of Jews from England in 1290 and from Spain in 1492, to the beginning of the First World War on the ninth of Av in 5674 (1914), to the sin of the extirpation of the Jewish communities of Gaza and northern Samaria in 5765 (2005).
And just as every major sin and punishment in the desert was followed immediately by the comfort of sacrifices with their concomitant atonement and forgiveness, so too we can draw comfort from the knowledge that almost as soon as the Three Weeks of mourning and punishment are over, we enter the month of Ellul, the month of preparing for the repentance, atonement and forgiveness of Rosh HaShanah and Yom Kippur. This is when God once again cradles us in His arms, lovingly granting us forgiveness, echoing year after year His words to Moshe (Numbers 14:20) on that first ninth of Av, when the spies returned from their doomed mission: Salachti kid'varecha - "I have forgiven, according to your words."