Tawheed and what is it?

 Tawheed and what is it? 

Alhamdulillah, 

Tawheed means to submit to Allah entirely that he alone deserves worship 

A person can never be a muslim or the islam of a person cannot stand without tawheed which is one God. 

This message was the reason the prophet muhammad salla Allahu alayhi wasalam with his companions were abused, beaten and driven out of makkah, losing their wealth and everything. 

To worship Allah only and making worship sincerely for him. 

Allah says in Quran, 

Az-Zumar 39:3

Unquestionably, for Allāh is the pure religion.[1] And those who take protectors besides Him [say], "We only worship them that they may bring us nearer to Allāh in position." Indeed, Allāh will judge between them concerning that over which they differ. Indeed, Allāh does not guide he who is a liar and [confirmed]

 disbeliever.

As we know the Arab pagan in Arabian peninsula knew Allah but do not believe he alone is to be worshipped, called upon in calamity except they associate partners with him like Lat, Mannay, Uzza, Baal and the rest. 

Allah says, 

An-Najm 53:19

So have you considered al-Lāt and al-ʿUzzā?

An-Najm 53:20

And Manāt, the third - the other one?[1]

An-Najm 53:21

Is the male for you and for Him the female?

An-Najm 53:22

That, then, is an unjust division.[1]

An-Najm 53:23

They are not but [mere] names you have named them - you and your forefathers - for which Allāh has sent down no authority. They follow not except assumption and what [their] souls desire, and there has already come to them from their Lord guidance.

The pagans used to call Lat, Mannat, Uzza as daughters of Allah and associate him with them while they too do not like female children. 

So such was unjust to Allah to have female daughters and for them male. 

So these are the shirk they used to commit in worship for rabbaniyyah of Allah like the creator, the provider, the one who gives life and death. 

But the ilaahiyah of Allah they disbelieved that he alone is to be worshipped without anyone like how christians associate Allah with jesus in worship..