Moshe Rabbeinu wanted to make it clear to the Jewish people, that although many religions would come into being, none would be able to compare with the truth of Judaism. His major point is repeated in the Kuzari, written by Rav Yehuda Halevi. In that book, we learn of a king that is searching for truth. He consults Greek philosophers, Christianity, and Islam.
When the king searches for a religion to observe, he starts with the obvious question as to how the religion began. Moshe’s point was irrefutable. He simply pointed out that no religion ever began with signs and wonders, and one nation taken out from the midst of another nation, as Judaism. And this was followed by a revelation, where every Jew actually heard G-d speak.
In the Kuzari, this impressed the king, to the extent that he and his entire kingdom converted. And it certainly should impress upon us that we are so fortunate to be part of Am Yisrael. Gradually, the world will acknowledge that G-d and the Torah, are the only real truth.