All the prophets sent by Allah SWT came with the unique message from Allah SWT, and that was,
There is no God but Allah and also that people are not allowed to follow any other entity except Him in any way.
The first 13 years of the Prophet of Islam in Makkah are significant when we talk about how important is the concept of monotheism in Islam. The Prophet of Islam Hazrat Muhammad SAW, preached this very concept from the beginning by the order and grace of Allah SWT and ordered people not to worship instead of Allah, the one and only God of the universe.
Prophet of Islam emphasized the importance of Tawheed from the very childhood, for that there is a hadith from Tirmizi, Prophet SAW said to Abdullah ibn Abbas, “When you ask, then ask Allah, and when you seek help, then seek help from Allah.” (Tirmidhi)
The distrusting Quraysh offered the Messenger of Allah Prophet Muhammad SAW, harmony, majesty, riches, and spouses and other than that from the delights of this life in return for him surrender the call to tawhid, and asked Him not to speak against their false idols. In any case, Prophet (PBUH) didn’t want that from them, rather lie proceeded with his call and persevered through the attack alongside his Companions, until the call to tawhid was successful following thirteen years, after which Makkah was free from such bad norms and the idols were annihilated.
What the Quran says about Monotheism
Say, “He is God, the One.God, the Absolute.He begets not, nor was He begotten.And there is nothing comparable to Him.” (Surah Ikhlas, 112)
“We have not sent before you from the Messengers, except We inspired to him that He is the only One worthy of worship, so worship Him.” (Al-Quran 21:25)
“Say: Verily I call to my Lord and I do not ascribe any partners to Him at all.” (Al-Quran 72:20)
“Indeed, We sent Nuh (Noah) to his people, and he said: “O my people! Worship Allah! You have no other Ilah (God) but Him. Certainly, I fear for you the torment of a Great Day!” (Al-A’raf 7: 59)
“And verily, We have sent among every Ummah (community, nation) a Messenger (proclaiming): “Worship Allah (Alone), and avoid (or keep away from) all false deities” Then of them were some whom Allah guided and of them were some upon whom the straying justified. So travel through the land and see what the end of those who denied (the truth) was.” (An-Nahl 16:36)
How Hadith Rasool SAW guides us for Monotheism
Mu’adh bin Jabal reported: The Prophet, peace, and blessings be upon him, said, “O Mu’adh, do you know what is the right of Allah upon His servants?” I said, “Allah and his messenger know best.” The Prophet said, “To worship Him alone and to associate none in worship with Him. And do you know what is their right upon Him?” I said, “Allah and his messenger know best.” The Prophet said, “Not to punish them if they do so.” (Ṣaḥīḥ al-Bukhārī 6938, Ṣaḥīḥ Muslim 30)
Key Factors why it is the Most Significant Aspect
Monotheism(Toheed) is one of the main pillars of a Muslim’s life. If a Muslim does not believe in the oneness of Allah and even if he has doubts in any way, and he shares the attributes of Allah SWT with any other creatures of this universe, a prophet, some saints or the places, he is not altogether a Muslim, no matter his name is Abdullah, Abdul Wali, or Muhammad bin Ahad bin Turab. So this is the key aspect and one has to make it as the base for his Emaniat, along with his belief that Muhammad SAW is the last prophet from Allah SWT.
Secondly, the purpose behind the creation of this universe is also to worship Allah only. As Allah says in the Quran
“And I (Allah) have not created the jinn and mankind except that they should worship Me (Alone).” (Quran, 51:56)
So Monotheism is the very purpose behind the creation of this universe.
Third and the foremost thing is to negate its opposite that is polytheism(shirk) in any way. As before the advent of Islam, there were 360 idols including Laat Manaat and Uzza in the holy Kaaba, and this was totally unacceptable by Allah SWT, so He with the message of Islam and Prophet SAW’s teachings eradicated this sin from the lives of the people and warned the people about the consequences of committing this hideous sin. As Allah says in the Quran,
“Indeed, he who associates others with Allah – Allah has forbidden him Paradise, and his refuge is the Fire. And there are not for the wrongdoers any helpers.” (Quran, 5:72)
There are more types of shirk as well, according to Prophet SAW, anyone who is show off and tries to tell about his goods just to gain some worldly benefits is called minor shirk.
So we can conclude by adding a few more lines that Monotheism that is totally opposite of the polytheism is the very essence and core thing in Islam and for Muslims. And there is zero-tolerance for such a sensitive issue. Allah may forgive all sins of his humans but not being monotheistic and being polytheistic is totally unacceptable in any way and in any form whatsoever.
May Allah forgive us all and help us being the believers in the oneness of Allah SWT till the last day of our lives. Aameen!