Categories of Tawhid
There are three main types of tawhid, namely Tawhid ar-Rububiyah, Tawhid al-Asmaa was-Sifaat, and Tawhid al-'Ibadah.
Tawhid ar-Rububiyah (Maintaining the Unity of Lordship)
In introducing this category of tawhid, Abu Aminah Bilal Philips writes This category is based on the fundamental concept that Allah alone caused all things to exist when there was nothing; He sustains and maintains creation without any need from it or for it; and He is the sole Lord of the universe and its inhabitants without any real challenge to His sovereignty. In other words, Allah reigns supreme over all that exists, has existed, or will exist.
This doesn't just mean recognising the Lordship of Allah in terms of sheer power, but also recognising that Allah is responsible for all that happens within the universe, no matter whether we consider it good or bad. Everything that happens occurs by the will of Allah alone, not by luck or chance.
The Second Category Of Tawhiid Is::
Tawhid al-Asmaa was-Sifaat (Maintaining the Unity of Allah's Names & Attributes)
This area of Tawhid has a number of aspects. Firstly, Allah should only be referred to according to what is written in the Qur'an, or how the Prophet Muhammad (SAW) referred to Him, as written in any of the hadith collections.
Secondly, Allah must not be given any attributes of any created being. For example, there are numerous examples in the Bible where Allah is given human attributes, such as fatigue and regret.
Thirdly, created beings should not be given any of the names or attributes of Allah. One example of this is a fortune-teller who claims to see the future, yet knowledge of the future is something which only belongs to Allah. This also means that to name yourself using one of Allah's names unless it is preceded with Abd' or Abdul, meaning slave or servant. For example, it is haram (forbidden) to name oneself 'Ar-Rahim' (the Most Merciful), but it is okay to use the name 'Abdul-Rahim' (servant of the Most Merciful).
The Third Category Of Tawhiid Is: :
Tawhid al'Ibadah (Maintaining the Unity of Worship)
This area of Tawhid is probably the most obvious one, as it ensures that any act of worship is directed at Allah alone, and not towards any people or objects (for example, the sun). It was this message which every one of Allah's prophets brought to their people.