Imam Ali (a.s.) in Nahjul-Balagha says:
The foremost in religion is the knowing of Him, the perfection of knowing Him is to believe in His Oneness, and the perfection of believing in His Oneness is to be sincere to Him."(46)
Belief in Allah, the One, and the Only, to Whom all the attributes of perfectness are ascribed and Who is above all the attributes of imperfection, is the main origin and base of the Islamic faith, thought, legislation and conduct...etc.
Therefore, the Imams of Ahlul-Bait (a.s.) gave more importance to form a pure concept of monotheism free from doubts, perversions, and disbelief of pre-Islamic ignorance and the remnants of pagan thought and strived hard towards correcting such thought by explaining the true meanings and faith of monotheism as proved by the Qur'an.
For more details, we cite some narrations of Ahlul-Bait (ass.) concerning the true meanings of monotheism and its concepts.
Imam Musa bin Ja'far (a.s.) wrote to one of his companions and said:
Verily, Allah is High, and Mighty (Sublime) and Great and far above that the reality of His attributes should be comprehensible. Assign to Him only those attributes that He ha s assigned to Himself and refrain from qualifying Allah with anything besides those attributes."(47)
Regarding the Almighty's integrity and the purity of Islamic thought from polytheism and paganism, the Ahlul-Bait (a.s.) narrated:
Whoever likens Allah with His creatures is a polytheist; surely Allah is the Almighty and High. Nothing resembles Him and nothing is like Him, and He is totally the reverse of whatever is imagined."(48)
One of the companions of Imam Ja'far bin Muhammad al-Sadiq (a.s.) asked him about the correct sect in monotheism, He (a.s.) said:
You - may Allah be merciful to you - asked me about monotheism and what that group of people believe in. Exalted is Allah, the like of whom there is naught, and He is All-Hearing and All-Seeing: Allah is above what is attributed to Him by those describers who liken Allah to His creatures, those who are slanderous to Allah. Know you - may Allah be merciful to you that in respect to monotheism, the true doctrine is what is revealed in the Qur'an about the attributes of Allah, the Almighty, the Exalted. Attributed not to Allah, the Sublime, any ideas of nihilism and similitude. Neither should His existence be negated nor should He be likened (to anything). He is Allah, the Established the Existent. Exalted is He far above what the false interpreters attribute to Him. Exceed not the Qur'an or you will go astray after the clear exposition of truth."(49)
Thus, the Imams of Ahlul-Bait (a.s.) explain that the true monotheism is the one called upon by the Qur'an which unified Allah in His Self, His attributes, His deeds and His worships.