As he moves from topic to topic, Moshe’s lectures sometimes seem to pose problems of cohesion. It then falls to our commentaries to explain the connections. An example of this is found in the first part of VAETCHANAN.

First, Moshe pleads before Hashem
Let me cross over and I will see the good land that is across the Jordan (Devarim 3:25).
Only part of his request would be granted, however: he would see the land from afar, but not make the passage.

Having brought his listeners to the effective end of the events of the wilderness, Moshe returns to its high point, the Revelation at Sinai:
The day when you stood before Hashem, your G-d, at Chorev, when Hashem said to me, “ Gather the people to Me, that I might make them hear My words, whereby they might learn to fear Me all the days that they live upon the land, and they shall teach their children” (4:10).

Consequently, Moshe exhorts his people to be especially on their guard against idolatry:
Guard your souls very carefully, because you did not see any image on the day Hashem spoke to you at Chorev from the midst of the fire. Lest you act corruptly and make yourselves a statue of the image of any form whatsoever. …And lest you raise your eyes heavenward and see the sun, and the moon, and the stars — all the host of the heavens — and you stray and prostrate yourselves to them and serve them, which Hashem, your G-d, apportioned to all the nations under the entire heaven. Whereas Hashem has taken you, and brought you out of the iron crucible, Egypt, to be His nation of inheritance, like this day (4: 15-16; 19-20).

Despite the (underlined) difficulties (of which more shortly), these ideas flow logically. However, at this point, Moshe inexplicably departs from his topic:
But Hashem became furious with me because of you, and He swore neither to let me cross the Jordan, nor to come to the good land that Hashem, your G-d, gives you as an inheritance. Because I will die in this land, I am not crossing the Jordan. But you are crossing, and you will take possession of this good land (4:21-22).

Afterwards, Moshe does revert to his initial themes to conclude the passage:
Be very careful lest you forget the covenant of Hashem, your G-d, that He made with you, and make yourselves a statue of an image of anything which Hashem, your G-d, has forbidden you. Because Hashem, your G-d is a consuming fire, a jealous G-d (4:23-24).
But, why the excursus in verses 21-22 that reiterates the Divine decree of his death?

Ramban answers simply that Moshe has carried out his mission of teaching the Israelites all the commandments that they are meant to fulfill in the land of Israel. However, since he will die on Mount Nevo he will not be able to continue teaching them. The Israelites will not be able to depend on the exhortations of their leader forever, so they themselves will have to take responsibility.

Sforno (R. Ovadia ben Yaakov Sforno, c. 1470-c.1550) explains more forcefully (4:22) that Moshe’s very passing might be the cause of the people’s backsliding:
“I need to caution you a great deal since I am not crossing with you. This is similar to what he says: For I know that after my death you will surely act corruptly” (Devarim 31:29).
After all, the first time the Children of Israel thought Moshe was dead they panicked and made the golden calf (Shemot 32)!

Keli Yekar (R. Ephraim Shlomo of Luntshitz, 1550-1619) takes this even further. The entire passage discusses idolatry:
And lest you raise your eyes heavenward and see the sun…
But, why should you, the people of Israel, be misled to worship the sun, when you are equal to the sun? As it says:
But those that love Him are like the coming out of the sun in its strength (Shofetim 5:31).
Moreover, you can even control the sun, as is seen in the battle of Giv’on (Yehoshua 10:1-14). The hosts of heaven are those, which
Hashem your G-d apportioned to all the nations under the entire heaven.
This means that the nations are subject to the influence of the planets. Hashem guides those nations indirectly,
Whereas Hashem has taken you
to rule over you directly. Therefore, it is absurd for you to want to worship the heavenly bodies.

Hashem
brought you out of the iron crucible, Egypt, to be His nation of inheritance, like this day;
He made you pure and clean as the clearness of the day.

Lastly, in order to explain the excursus beginning with
But Hashem became furious with me because of you,
Keli Yekar refers to an exchange recorded in the Talmud (Avodah Zarah 54b) between the “philosophers” and the Sages of Rome. The former said, “If your G-d does not want there to be idolatry, why doesn’t He abolish it?” The Sages replied, “If they would worship something that the world does not need, He would abolish it. But they worship the sun, the moon, the stars and the constellations. Should His world be destroyed because of the fools? Rather, let the world continue in its normal fashion, and those fools who go astray are destined to give an accounting.” (Compare with Rashi on this verse.)

Conversely, says Keli Yekar, when Moshe’s actions led the people to sin, Hashem was prepared to remove him. This is because his removal would not lead to widespread harm. Moshe’s continued presence could be an impediment to the people’s connection to Hashem, suggests Keli Yakar, because they might come to deify him.

Although, says Moshe,
I will die in this land, I am not crossing the Jordan, but you are crossing.
They must be true to Hashem’s dictates alone, without Moshe. The great and humble leader Moshe accepts Hashem’s decree, for the benefit of his beloved people.