The first directive is that since there is no god except God, only He should be worshipped. The essence of this worship (‘ibādah) is humility and modesty. The first manifestation of this essence is serving the Almighty. Since a person also has a practical life in this world, this servitude relates to this practical life as well and in this manner becomes inclusive of obedience. The manifestations in the first case are glorifying Him and singing His praises, praying to him and supplicating before Him, kneeling and prostrating before Him, making vows (to please Him), offering animal sacrifice and doing i‘tikāf.
In the second case, a person, after regarding someone as an independent law giver and ruler, considers that he has the authority to give directives of what is forbidden and what is not and what is allowed and what is not and submits before all his directives. It is the verdict of God Almighty that none of the above mentioned things can be reserved for someone other than Him. The words قَضَى رَبُّكَ أَلاَّ تَعْبُدُواْ إِلاَّ إِيَّاهُ declare this verdict. Thus if a person glorifies someone and sings his praises or prays and supplicates before someone, kneels and prostrates before him or presents vows before him or offers animal sacrifice to him or does i‘tikāf for him or regards him to have the authority of prohibiting or allowing things, then this would mean that he has refused to accept this verdict of God. Among the addressees of the Qur’ān those who were guilty of this sin were clearly told of their folly.
Those who prostrated themselves before the sun and the moon were told:
لَا تَسْجُدُوا لِلشَّمْسِ وَلَا لِلْقَمَرِ وَاسْجُدُوا لِلَّهِ الَّذِي خَلَقَهُنَّ إِن كُنتُمْ إِيَّاهُ تَعْبُدُونَ (37:41)
Do not prostrate yourselves before the sun or the moon; rather prostrate yourselves before God, who created them both, if you would truly serve Him. (41:37)
Those who prayed and supplicated before some of their ancestors were told:
وَالَّذِينَ يَدْعُونَ مِن دُونِ اللّهِ لاَ يَخْلُقُونَ شَيْئًا وَهُمْ يُخْلَقُونَ أَمْواتٌ غَيْرُ أَحْيَاء وَمَا يَشْعُرُونَ أَيَّانَ يُبْعَثُونَ (16: 20-21)
And those whom these call besides God are themselves created, they create nothing: They are dead, not living and don’t even know when they will be raised to life. (16:20-21)
Those who presented as sacrifice and vows, the produce and cattle created by God before other deities were warned thus by the Qur’ān:
وَجَعَلُواْ لِلّهِ مِمِّا ذَرَأَ مِنَ الْحَرْثِ وَالأَنْعَامِ نَصِيبًا فَقَالُواْ هَـذَا لِلّهِ بِزَعْمِهِمْ وَهَـذَا لِشُرَكَآئِنَا فَمَا كَانَ لِشُرَكَآئِهِمْ فَلاَ يَصِلُ إِلَى اللّهِ وَمَا كَانَ لِلّهِ فَهُوَ يَصِلُ إِلَى شُرَكَآئِهِمْ سَاء مَا يَحْكُمُونَ (136:6)
And they set aside a share of their produce and cattle for God. They then say that in their opinion: “This is for God and this is for those whom we associate with God.” Furthermore, the share of these associates does not reach God but the share of God can reach these associates. What an evil judgement they pass! (6:136)
Those who regarded their jurists and scholars to have the authority to declare something as lawful and something as forbidden were warned thus:
اتَّخَذُواْ أَحْبَارَهُمْ وَرُهْبَانَهُمْ أَرْبَابًا مِّن دُونِ اللّهِ وَالْمَسِيحَ ابْنَ مَرْيَمَ وَمَا أُمِرُواْ إِلاَّ لِيَعْبُدُواْ إِلَـهًا وَاحِدًا لاَّ إِلَـهَ إِلاَّ هُوَ سُبْحَانَهُ عَمَّا يُشْرِكُونَ (31:9)
They have made their scholars and their monks their Lord besides God and also Jesus, the son of Mary, even though they had been directed to worship one God only. There is no god but Him. Exalted is He above those they deify besides Him! (9:31)
The Qur’ān has thus regarded this authority to declare something as lawful or unlawful as baseless besides regarding as baseless the prohibitions stipulated by the Arabs for certain animals called bahīrah, sā’ibah, wasīlah and hām.
Bahīrah is the name given to a she camel which has five offspring, the last of which is a male. The ears of such a camel are slit and it is left free.
Sā’ibah is the name given to a camel which is left free once the vow regarding it has been fulfilled.
As for wasīlah, some people would vow that if a goat would give birth to male offspring, they would present it before their idols, and if gives birth to female offspring, they would keep it to themselves; now if she would give birth to male and female offspring simultaneously, they would call it wasīlah and would not present such male offspring to their idols.
Hām is the name of a bull which has given birth to many offspring. It would be left free.
The Qur’ān says:
مَا جَعَلَ اللّهُ مِن بَحِيرَةٍ وَلاَ سَآئِبَةٍ وَلاَ وَصِيلَةٍ وَلاَ حَامٍ وَلَـكِنَّ الَّذِينَ كَفَرُواْ يَفْتَرُونَ عَلَى اللّهِ الْكَذِبَ وَأَكْثَرُهُمْ لاَ يَعْقِلُونَ (103:5)
God has sanctioned neither a bahīrah, nor a sā’ibah, nor a wasīlah, nor a hām but these disbelievers fabricate falsehoods about God and most of them have no sense. (5:103)
It is this very verdict of the Qur’ān regarding the worship of God on account of which the Prophet (sws) forbade people from making graves places of prostration and said that may God curse the Jews and Christians for they have made the graves of their prophets as mosques.
The fact that this was his last counsel for the Muslims before his death shows its importance.