לֹ֧א אֲגָרְשֶׁ֛נּוּ מִפָּנֶ֖יךָ בְּשָׁנָ֣ה אֶחָ֑ת פֶּן־תִּהְיֶ֤ה הָאָ֙רֶץ֙ שְׁמָמָ֔ה וְרַבָּ֥ה עָלֶ֖יךָ חַיַּ֥ת הַשָּׂדֶֽה׃
I will not drive them out from before thee in one year, lest the land become desolate, and the beasts of the field multiply against thee.
Rashi on Exodus
שממה DESOLATE — empty of human beings, for you are but few and not sufficient to fill it all up.
Siftei Chakhamim
Is to be understood as ותרבה עליך . You might ask: Why does Rashi not explain here as he does later in Parshas Eikev (Devarim 7:22) on the verse, “Lest the wild animals multiply against you”? [For there he said,] “But behold, if they do the will of God then they need not fear the beasts. . . Rather, [the verse implies that] God knew they are destined to sin.” It seems that [Rashi did not say so here because] it is written here, “Lest the land become desolate and the beasts of the field multiply.” This implies that the verse is explaining that the many beasts are a result of the desolation of the land, [rather than being an allusion that they are destined to sin]. Another answer: Here it is written (v. 20), “Behold, I will send an angel. . .” on which Rashi explained, “Here they are foretold that they are destined to sin.” So Rashi does not need to explain this point again here.
Rashi on Exodus
ורבה עליך means, [LEST THE ANIMALS OF THE FIELD] MULTIPLY AGAINST THEE.