כִּ֛י חֵ֥לֶק יְהֹוָ֖ה עַמּ֑וֹ יַעֲקֹ֖ב חֶ֥בֶל נַחֲלָתֽוֹ׃
여호와의 분깃은 자기 백성이라 야곱은 그 택하신 기업이로다
Rashi on Deuteronomy
כי חלק ה' עמו FOR THE PORTION OF THE LORD, HIS PEOPLE — Why all this? (Why did He save them from destruction?) because His portion was comprised in them and was destined to come forth. And who is His portion? עמו HIS PEOPLE. And Who is His people?
Sforno on Deuteronomy
יעקב חבל נחלתו, for he as well as his sons became servants of the supreme G’d. By contrast, whenever there was a pious and G’d fearing individual among the gentile nations, such piety and belief in G’d was never transmitted to and carried on by the next generation.
Siftei Chakhamim
Because His portion was hidden among them, etc. Because the term כי (because) always explains what precedes it. So here too, it implies that Scripture wants to give an explanation of what preceded.