"So it is made clear with this, that the Ayaah (9:31) proves that whoever obeys other than Allaah and His Messenger and turns away from taking from the Book and the Sunnah, concerning making Halaal what Allaah made Haraam or making Haraam what Allaah made Halaal or obeys him in the disobedience of Allaah and follows him in what Allaah did not give permission for, then he has taken him as a lord and something worshipped and made him a partner with Allaah and that
contradicts the Tawheed which is the Deen of Allaah that the words of Ikhlaas: La Illaaha il-Allaah, have indicated. (This is) because the Ilaah is the thing, which is worshipped, and Allaah, ta'ala labeled their
obedience as worship towards them and called them lords.

Like He, ta'ala said: 'And He does not order you to take the angels and the Prophets as lords… ' In other words, '… as partners with Allaah in His worship… ' – 'Does He order you to do Kufr after you were Muslims? ' And this is the Shirk because anything which is worshipped is a Lord and all things, which are obeyed or followed concerning other than what Allaah or His Messenger have legislated, then he has been taken by the obedient one or the follower as a Lord and a thing to be worshipped.

Like He, ta'ala said in Surah An'am: 'And if you obeyed them,
then you are Mushrikeen. ' And this is the meaning of this Ayaah and like this Ayaah in meaning is His, ta'ala's saying: 'And do they have partners who have legislated in the Deen what Allaah did not give
permission for? ' And Allaah knows best."
– "Fat'h Al-Majeed", Pg. 110-111 Published by "Dar Al-Fikr"