Tawhid is the basis of the religion of Islam, and is a conviction and witnessing that most precisely expressed in the statement: la ilah illah Allah (There is no God but Allah) which states that there is only one true God and He alone deserves to be worshipped. This expression that differentiates a true Muslim from a kafir (unbeliever), mushrik (one who associates others with God in His Divinity) or dahryah ( an atheist).

MEANING OF TAWHID 

             1. Literally meaning:

            Tawhid means "unification" (making something one) or "asserting oneness", and it comes from the Arabic verb (wahhada) which itself means to unite, unify or consolidate.

               2. Technical meaning:

              When the term Tawhid is used in reference to Allah (i.e. Tawhidullaah), it means the realizing and maintaining of Allah's unity in all of man's actions which directly or indirectly relate to Him.

            It is the belief that Allah is One, without partner in His dominion and His actions (Rububiyah), One without similitude in His essence and attributes (Asma wa- Sifat), and One without rival in His divinity and in worship (Uluhiyah/'Ibadah). These three aspects form the basis for the categories into which the science of Tawhid has been traditionally divided.

            The three overlap and are inseparable to such a degree that whoever omits any one aspect has failed to complete the requirements of Tawhid, is referred to “Shirk” (sharing).

THREE CATEGORIES OF TAWIHD

1. Tawhid ar-Rububiyyah : "Main taining the Unity of Lordship"

2. Tawhid al-asma’wal-sifat :"Maintaining the Unity of Allah's Names and Attributes"   

3. Tawhid al-‘Ibadah :   "Maintaining the Unity of Allah's Worship"

            There is no being worthy of worship except Allah (God), and Allah is Absolutely One and Absolutely Unique. We note also that a Muslim is further obligated to accept the Prophet Mohammad (S.A.W) as Allah's final prophet to humanity. Faith in One God (Tawhid) in the teachings of the Prophet Mohammad is the bedrock of Islam and the mainspring of its power. All others beliefs, commands, and laws of Islam stand firm on this foundation. All of them received strength from this source.Take it away, and there is nothing left of Islam.