Ralph Waldo Emerson says, “ God is unity, but always works in variety ”
Nature manifests variety in abundance.
Evolutions establish variety.
Civilizations require unity.
Humane attitude enables humanity to understand the necessity for unity and also the inevitability of variety.
Unity must not be confused with uniformity or homogeneity enforced by any means.
The following link, along with many other links in it, explains in detail various aspects/facets of this single fact of unity amid variety.
The link below explores the inherent polarity in nature or as part of nature.
This polarity enables us to perceive the distinctions and differences and they are not meant to divide.
This link of course places on record some attempts made by various religions towards forging unity as a concept.