Read Surah Al-Ikhlas

فهو على هذا اسم لعين الذات، فيه سلب الكثرة عن ذاته، فتقدس به...

Thus, 'al-Ahad' is a name for the essence of God, implying the negation of multiplicity from His essence. This description thereby sanctifies Him from the attributes of bodies that are susceptible to division and separation, as well as from the concept of a point or an individual substance as posited by some theologians - referring to those who assert the existence of individual substances - and from the simple substance as claimed by philosophers. Although these concepts are indivisible and inseparable, they are still distinct from the Creator, may He be exalted, in terms of His oneness. The concept of a point, according to some, is an accident, as it is defined as the endpoint of a line; if a line is an accident, then a point is even more so. As for the individual substance, although it is indivisible, it is still quantifiable and, as such, is not devoid of accidents. Similarly, the simple substance, as conceived by its proponents, has an existence that is not identical to its essence when considered in a dual context, implying a duality in their conception. Thus, God, may He be exalted, is distinguished from these entities by His oneness, just as He is distinguished from bodies by His essence. His existence is inherent to His essence, and His attributes are not separate from His essence. On the other hand, 'al-Wahid' is a description of His essence, implying the negation of a partner or counterpart. The two terms are distinct in that 'al-Ahad' refers to the essence itself, while 'al-Wahid' refers to something external to it. Al-Bayhaqi, in his book 'Kitab al-Asma' wa as-Sifat', states that the term 'al-Ahad' cannot be applied to anything that the polytheists consider a deity besides God.