Two contractors came to talk to us about our remodel. Their company was called "Siblings," and they said they were "brothers in Christ." They used that term to differentiate themselves from people like me. If they'd wanted to include me, they could have said that we're all "God's children."
Sometimes you hear Christians talking about God, and sometimes you hear them talking about Jesus. Liberal Christians like to talk about "God" and conservative Christians like to talk about "Christ." Why? Because Christ is exclusive.
A Christian can talk about "God" and feel themselves part of a worldwide family of faith. Jews, Muslims, Christians all believe in the One God, and many people of other faiths also worship a Supreme Being, Great Spirit, or other ultimate divinity. But when a Christian talks about Jesus, they differentiate themselves from that greater community. The idea of God is global, universal, and approachable from several directions. He is perhaps even ineffable enough to allow certain variants in interpretation. But Jesus is historical, local, particular, even ethnic. The idea of God unites Christians with non-Christians. The worship of Jesus separates Christians from non-Christians. Christians can talk about their understanding of God as part of their tradition and culture, something to be valued just as others' traditions and cultures are to be valued. But when they talk about Jesus as part of the trinity and as the one without whom no one is saved, then they're treating their tradition as the truth that's right for everyone.
When they say that we are all "God's children," they're including everyone. When they say that they are "brothers in Christ," they're excluding most of us.
One can also see this preference for "God" over "Christ" in popular media going back decades.
Jesus Christ is the special thing that only the Christians have. He is the special way for Christians to think of themselves as right and others as wrong. He is their key to denying that other believers are their equals.
Is this divisiveness unique to Christianity? By no means. Does it mean that Christianity is a worse or more close-minded religion than average? No. The distinction between talking about "God" and about "Christ" is just a noteworthy phenomenon that marks how far post-modernism has and has not spread.