The Keli Yakar explains: We have found that
sometimes Hashem compares Israel to the stars and sometimes to the sand on the shore of the sea …. As in times of tranquility and success, He compares them to the stars. That is an expression of greatness, as Rashi explains in this weeks Perasha. And the comparison of the sand indicates the time when the nations rise up against Israel to destroy them, but they cannot [defeat] them. This is like the waves that go up as if they wanted to flood the whole world. But immediately when they reach the sand, they are
broken. So too are the nations.  

 Rabbeynu Bachya takes a Midrashic approach, found in Devarim as a reference to the encampment of the Jewish people, and are similar to when G’d showed Avraham that all the zodiac signs in heaven surrounded the Shechinah. Similarly, the flag of the Jewish people, three tribes and their flag in each direction is perceived with the Shechinah in the center of the camp. Hashem had told Moses: “just as the zodiac signs surround Me and I am in the center, so your children will multiply and encamp according to their respective flags while My Presence will dwell in their midst.  

 For me the most interesting comment is from the Shnai Luchot HaBrit where Rabbi Horowitz comments 'You are today as numerous as the stars in the sky,' he immediately added a blessing, i.e. 'May the Lord the G–d of your fathers increase your numbers a thousand fold, and bless you as He promised you.' This verse contains two blessings: Moses blessed G–d, Moses asking G–d to bless Israel.'