Regarding these 13 principles I prefaced some remarks on the parent page here
The fifth of the Rambam’s principles is that G-d is the only one that it is fitting that we serve Him and worship Him, to exalt Him, and to tell others about His Greatness. Therefore one should not do such worship to anything below G-d, whether it is in the Heavenly realms like the angels or the stars, or anything in this worldly realm below, or anything which is built from them.
The reason for this is that all of them were created by G-d, each with its own limitations in its ability to act, no one and no thing has command power nor free choice to do anything on his own, just that which G-d lets him do.
Additionally, one should not worship these other things as a vehicle to worship G-d, rather all of his intentions and thought should be to serve G-d alone and nothing else.
This fifth principle in essence is the prohibition of idol worship about which the Torah is full of exhortations and warnings.
