We live in succession, in division, in parts, in particles. Meantime within man is the soul of the whole; the wise silence; the universal beauty,

The Supreme Critic on the errors of the past and the present, and the only prophet of that which must be, is that great nature in which we rest, as the earth lies in the soft arms of the atmosphere; that Unity, that Over-soul, within which every man's particular being is contained and made one with all other; that common heart.

For Emerson the term denotes a supreme underlying unity which transcends duality or plurality, much in keeping with the philosophy of Advaita VedantaAdvaita Vedanta
Advaita is more often than not deviantly interpreted as monism/monistic system of thought. Advaita Vedanta is a sub-school of the Vedanta school of Hindu philosophy....
. This non-Abrahamic interpretation of Emerson's use of the term is further supported by the fact that Emerson's Journal records in 1845 that he was reading the Bhagavad GitaBhagavad Gita
The Bhagavad Gita is an important Sanskrit Hindu scripture. It is revered as a sacred scripture of Hinduism, and considered as one of the most important religious classics of the world....
and Henry Thomas ColebrookeHenry Thomas Colebrooke
Henry Thomas Colebrooke was an England orientalist....
's Essays on the VedasVedas
The Vedas are a large body of texts originating in History of India. They form the oldest layer of Sanskrit literature and the oldest Hindu scripture of Hinduism....
. Emerson goes on in the same essay to further articulate his view of this dichotomy between phenomenal plurality and transcendental unity:

We live in succession, in division, in parts, in particles. Meantime within man is the soul of the whole; the wise silence; the universal beauty, to which every part and particle is equally related, the eternal ONE. And this deep power in which we exist and whose beatitude is all accessible to us, is not only self-sufficing and perfect in every hour, but the act of seeing and the thing seen, the seer and the spectacle, the subject and the object, are one. We see the world piece by piece, as the sun, the moon, the animal, the tree; but the whole, of which these are shining parts, is the soul.