"פֶן-תִּשָּׂא עֵינֶיךָ הַשָּׁמַיְמָה, וְרָאִיתָ אֶת-הַשֶּׁמֶשׁ וְאֶת-הַיָּרֵחַ וְאֶת-הַכּוֹכָבִים כֹּל צְבָא הַשָּׁמַיִם, וְנִדַּחְתָּ וְהִשְׁתַּחֲוִיתָ לָהֶם, וַעֲבַדְתָּם--אֲשֶׁר חָלַק ה' אֱלֹקיךָ, אֹתָם, לְכֹל הָעַמִּים, תַּחַת כָּל-הַשָּׁמָיִם."
"... and lest thou lift up thine eyes unto heaven, and when thou seest the sun and the moon and the stars, even all the host of heaven, thou be drawn away and worship them, and serve them, which the LORD thy God hath allotted unto all the peoples under the whole heaven." (Devarim 4:19)
What's meant by "allotted by G-d unto all the peoples under the whole heaven", and why is it necessary to say so in relation to the prohibition to bow down for those and serve them?