The lower-tier state university I attended had creepy "Unity in Diversity" Soviet posters all over the place. The only creepier public ad I've seen is the lyrics to "Imagine" on a ticker in Picadilly Circus.
But invert the phrase and you have a good description of the Church: Diversity in Unity. Ok, maybe a bit slogan-y and trite, but thinking in Epiphany terms:
1. The Gospel is for all people, all tribes, all nations. Christ died not just for the Jew, but for we poor Gentiles, too. He didn't just die for the elect, but for all of humanity. We are to "teach all nations" (Matt 28:19), Christ is the "Desire of all Nations" (Hag 2:7), through Abraham, in Christ "All the nations will be blessed" (just go read all of Galatians 3). We are Christ's body, and one in him, regardless of ethnic, sex, or economic differences. We are united to Him (and therefore to each other) in baptism.
2. Christianity is not Hinduism. We are not not losing our individual self in a sort of Platonic pantheism. Material is good (God said so, when he made it). But material, by nature, divides and separates. I am not you, although I am one with you in Christ, if you are baptized. When we are all glorified, we will still be individuals, distinct from each other. We are diverse.
I think a good doctrine of the Trinity helps understand the Christian "Diversity in Unity." Meditate a bit on the precise wording of the Athanasian Creed. Like the Trinity (I say this with no impiety intended), we are one (because of our baptism, and being members of Christ's body), yet retain our personhood.
So how does this translate into practice? I love visiting a church where I know when to stand and sit, what to expect in a sermon (Law and Gospel, baby!), and I recognize the ordinaries. Even when attending my in-law's conservative Reformed Baptist church, I recognize the skeleton of a traditional liturgy. They have a call to worship, Psalm, Bible reading (distinct from the sermon), a sermon hymn, and "prayers of the church." It's not a Divine Service (no communion on Sunday morning, ever!), but I know what to expect. When I attended Roman Masses abroad I loved hearing the Our Father and Nunc Dimittis, although spoken in French, Italian, or Latin. I could follow the service because I knew the outline of a traditional liturgy, and I could hear the familiar inflections (Christians everywhere seem to say the Our Father the same way). I'm not promoting a shallow ecumenism, only pointing out the comfort of unity and consistency. It's good to know when you're in church.
But I also love attending congregations when they are celebrating a local anniversary or custom. The local church, while part of the church universal, has its own history and particular traditions: special Easter brunches or other annual meals, services of thanksgiving for regional blessings (perhaps a good harvest), or prayer services during local disaster, and any number of little yearly observances.
So how can we practice diversity in unity in the home?