If we analyze our lives from a Vedantic point of view, then we would realize that the manifest plurality of world basically indicates towards one supreme reality, Brahman. What is it that we see in the world? Only two things, sentient beings and insentient objects! If it can be proved that both are none other than Brahman, then it will basically entail that only Brahman is the reality.
Vedanta proves it by giving a wonderful analogy. It states that sentient beings are made up of Atman and matter. Atman is present everywhere like sunlight. There is only one sunlight which is present everywhere. However, if there are numerous mirrors, then we are able to see different individual suns. The individual suns are conditioned by the quality of mirrors. If mirror is blue, the sun shall be blue. If mirror is dirty, the sun shall be dirty. Similarly, the numerous sentient beings can be compared to mirrors. The gross body is the frame of mirror in which mirror is situated. Subtle body, i.e. mind and intellect are glasses of mirrors. The causal body, i.e. Vasanas is basically the polish of mirror. Thus, the one omnipresent Atman reflects itself in numerous mirrors and gives rise to several individual conditioned Atman. This conditioned individual Atman, which is nothing but the reflection of Atman in mind-intellect equipment, is given a name in Vedanta. It is called ‘Jiva’ or ‘Ahamkara’. Though the Atman doesn’t have any properties or attributes, this jiva or ahamkara has several properties. It is localized and it is this, which creates the feeling that body, mind and equipment belong to it. Thus, when we say my body, my mind and my intellect, the ‘I’ refers to Ahamkara.
It is important to understand as to how wonderful this analogy is. The corollary of this analogy will be extinguishment of ahamkara if the polish, i.e. Vasana is removed. Then, the Atman shall go through the mind-intellect without an ahamkara being created. Thus, it is said that with extinguishment of Vasanas, ahamkara also dies. The destruction in ahamkara is basically called moksha, which is the aim of Vedanta.
Thus, Vedanta proves that the manifest sentient beings, acting differently, are basically the reflection of only one Atman through different mind-intellect-vasanas. Thus, the innumerable ahamkaras are basically only one Atman. And therefore there is only one reality in diverse plurality of sentient beings.