Kommentar zu Dewarim 3:18

ואצו אתכם AND I COMMANDED YOU — He now addresses himself to the sons of Reuben and the sons of Gad.

ואצו אתכם בעת ההיא, ”I commanded you at that time, etc.” Moses was now speaking to the tribes of Gad and Reuven. Seeing that they were part of the people of Israel, Moses used the pronoun אתכם, “you,” as if his commandment applied to all the tribes. Actually, it would have been less misleading if he had used the pronoun אותם, “them.” (compare Ibn Ezra). We find something similar at the end of the Torah where Moses “officially” addresses the Levites (Deut. 31,25-27) commencing with “Moses comman-ded the Levites ... to take the Torah scroll and to place it at the side of the Ark; “I have known your rebelliousness and stiff neck, etc.” Although Moses is reported as speaking to the Levites, he addresses the whole people. [The Levites most certainly did not have an exclusive on being rebellious, rather the reverse. Ed,]

He was speaking to Bnei Reuvein and Bnei Gad. Rashi is answering the question: The rebuke from the beginning of this book until now was all directed at the entire Bnei Yisroel. But how can, “Cross over in the forefront ahead of your brothers Bnei Yisroel,” be referring to the Bnei Yisroel? Is it possible for Bnei Yisroel to cross over ahead of Bnei Yisroel?! Rashi therefore explains: He was speaking to Bnei Reuvein and Bnei Gad.