Deuteronomy 4:25

If, when thou wilt have begotten children and children’s children, and wilt have grown old in the land, you corrupt your works, and make to you an image or any likeness, and do that which is evil before the Lord to provoke Him;

After describing God as a “jealous God” [: 24] Scripture now explains what will happen to them if they make idols

or do evil concerning any of the other commandments, like murder or adultery.

KI’ (WHEN) THOU SHALT BEGET CHILDREN, AND CHILDREN’S CHILDREN, AND YE SHALL HAVE BEEN LONG ESTABLISHED IN THE LAND. The purport of this verse is that it mentions and affirms that “when ye shall beget children and children’s children, and because you will have been long established in the Land and dwelled in security, you may perhaps forget G-d — I call heaven and earth to witness against you this day], but instead they constitute one statement, as follows: “Should a longer period of security in the Land create a tendency among the people to idolatry, heaven and earth will witness Israel’s loss of the Land.” that ye shall speedily perish, for He will not be long-suffering with you seeing that you worshipped idols.”
Now this section, although constituting a warning, opened [with the word ki — “when” and] not with the expression im — “if” [which would be here more appropriate, since it speaks of a hypothetical condition of future time]. The reason is that he [Moses] was virtually prophesying about their affairs, and therefore he spoke in an equivocal manner — using an expression which in addition to being a warning [to avoid the sin of idolatry] also contains a prediction of things to come [when the warning will not be heeded]. He was thus saying that if they do so the following will happen to them, but he does not decree that they will do it. Therefore our Rabbis have said that in the numerical-value of [the letters in the Hebrew word] v’noshantem (and ye shall have been long established) is equivalent to 852 [vav = 6; nun = 50; vav = 6; shin = 300; nun = 50; tav = 400; mem = 40; — totalling 852]. Thus at the end of 852 years from the time that Israel came into the Land the exile was to occur. G-d, however, brought this about two years earlier in order that the prophecy — they shall “utterly perish” — at the end of that period should not come to pass. By bringing about the exile two years before the terminus of 852 years, G-d voided the prediction of total retribution. — It is of interest to note that in his Sefer Hage’ulah (Book of Redemption) Ramban similarly writes of the future redemption that, after it will have occurred, the allusion to that date will be found in this section of the Torah (Kithvei Haramban, Vol. I, p. 263). he alluded to the time of the exile following the destruction of the First Sanctuary. It was thus a tradition [among the prophets and Sages of the generations] that this section of the Torah contains an allusion to the time of the exile, and, when it actually came to pass, they understood the allusion by contemplating this section [and interpreting the hidden message of the prophecy in light of the historical event].

להכעיסו, to cause the benevolent presence of G’d to remove it self from Israel, in order to clear the way for the people to be just like the gentile nations, free of the yoke of the Torah’s commandments.

כי תוליד בנים וגו, “when you beget children etc.” Moses warns the people not to take their settlement in the land of Israel for granted even after they have lived there for several generations. Their tenure in the land is contingent on their continuing to observe the Torah and all of its commandments. If they failed to do, not only would they endanger their tenure of the land, but they would endanger their continued existence as G–d’s people. [If, say after six generations in the Holy Land, the people who had not been witnesses to all the miracles G–d had performed before the first generation settled in that land, they would claim that there was no reason why their tenure is linked to Torah observance, just as their neighbour’s tenure to their respective lands is not contingent on a set of laws of their religion, Moses warns them against such a fatal error. Ed. According to the Talmud, tractate Sanhedrin, folio 38, the numerical value of the letters in the words: ונושנתם בארץ, “and you will be long established in the land,” (852) אבוד תאבדון, “you will be utterly wiped out in verse 26. G–d did us a great favour when the exile began after 850 years of tenure, so that the threat of utter destruction of the Jewish nation since the time Joshua crossed the Jordan did not have to be fulfilled. This has been hinted at in the Book of Daniel 9,14: וישקוד ה' על הרעה ויביאה עלינו כי צדיק ה' אלוקינו, “Hashem hastened the calamity and brought it upon us, for Hashem is righteous in all He does (but we did not heed His voice).”