To be “common” is to be of frequent occurrence; the normative, the usual, simply normal. Two or more people can hold a thing “in common,” making it general commodity. We’ve heard of “common knowledge,” describing something that the majority should generally know. We hear a lot about so-called “common sense,” which isn’t very common and doesn’t make much sense anymore. A group of people could have a “common belief;” a shared belief system that gives identity to and is very important for the group of individuals that hold it. The idea of “common” also expands into mathematics, speech, grammar, anatomy, and law, etc. but the meaning doesn’t drift far from the original intent.
“Unity” is a state of being one; oneness. To speak of “unity” infers combined parts; two or more parts have come (or were put) together to form one whole. Often the ideology of “unity” (oneness) takes on the notion of sameness; that there is no diversity in the sum whole of the parts. Two or more people could come to an agreement and, therefore, be said to be in “unity.” Again, the idea of “unity” (or not) has been adapted to mathematics and the arts, etc.
A “Community” is a social group of two or more that may share a common language and/or culture and/or rules and/or beliefs and/or heritage and/or locale having a unity in a common life. Sometimes a “community” purposely lives thusly to distinguish itself from others. A place where two or more things live could be a “community.” The understanding of “community” pervades law and the sciences, etc.
God is a “community” – a trinity – within God’s-self. Humanity derives from the “God-community.” From the whole came the parts (i.e., creation), and the parts are called to become one in the whole (salvation). In this in-between place – the now, but not yet – we are “united” in a “common” calling: Humanity as a whole, and not distinct from its parts, is called to live in “community.” There is diversity, by definition, because of its parts – differing races, cultures, rules, heritage, language, and etc. – but diversity is not contrary to oneness, but only sameness. It is the power of God’s Spirit in the Person of God’s grace – Jesus Christ – that unites this diversity in “community.”
“Community,” then, in one sense is “common” – we hold the Source of community and the humanness of community in common. Ironically, though, the “common sense” required for this “common knowledge” has been lost on humanity, generally. Therefore, on the other hand, life together as “community” is not a frequent occurrence. Likewise, “Community” is a shared wholeness of its combined parts. “Unity” is an agreement between differing parts to being part of the whole “community.” Then again, “community” is not one part(s) forcing its own race, culture, rules, heritage, language, and etc. onto the other part(s) and calling it “unity.” God’s grace “unites” the differing “common” parts into one whole “community” sharing the life of God’s Common-Unity. Like putting a whole puzzle back together, all the individual parts (each with their peculiar shapes) must be utilized in order to return to the puzzle’s whole picture.