Allah's statement,
﴿وَإِنْ أَطَعْتُمُوهُمْ إِنَّكُمْ
لَمُشْرِكُونَ﴾
(and if you obey them, then you would indeed be polytheists.) means, when you turn
away from Allah's command and Legislation to the saying of anyone else, preferring
other than what Allah has said, then this constitutes Shirk. Allah said in another
Ayah,
﴿اتَّخَذُواْ أَحْبَـرَهُمْ وَرُهْبَـنَهُمْ
أَرْبَاباً مِّن دُونِ اللَّهِ﴾
(They (Jews and Christians) took their rabbis and their monks to be their lords
besides Allah.)﴿9:31﴾ In explanation of this Ayah, At-Tirmidhi recorded that `Adi
bin Hatim said, "O Allah's Messenger! They did not worship them.'' The Prophet said,
«بَلَى إِنَّهُمْ أَحَلُّوا لَهُمُ
الْحَرَامَ وَحَرَّمُوا عَلَيْهِمُ الْحَلَالَ فَاتَّبعُوهُمْ فَذَلِكَ عِبَادَتُهُمْ
إِيَّاهُم»
(Yes they did. They (monks and rabbis) allowed the impermissible for them and they
prohibited the lawful for them, and they followed them in that. That was their worship
of them.)
﴿أَوَمَن كَانَ مَيْتًا
فَأَحْيَيْنَـهُ وَجَعَلْنَا لَهُ نُورًا يَمْشِي بِهِ فِى النَّاسِ كَمَن مَّثَلُهُ
فِي الظُّلُمَـتِ لَيْسَ بِخَارِجٍ مِّنْهَا كَذَلِكَ زُيِّنَ لِلْكَـفِرِينَ مَا كَانُواْ
يَعْمَلُونَ ﴾
(122. Is he who was dead, and We gave him life, and set for him a light, whereby
he can walk among men -- like him who is in the darkness from which he can never
come out Thus it is made fair seeming to the disbelievers that which they used to
do.)