“I have not come to bring peace, but a sword.”
The Lord Jesus came to create division, and when he returned to his Father, he left us with the division his visit, his person and his claims created. Those who have believed in him enjoy a unity and a commonality previously unimagined, which we sometimes call fellowship. But the difference between his children and those who are not his own is the difference between light and darkness, between righteousness and lawlessness, and between Christ and Belial.
That is not always apparent. It is especially not apparent to those in darkness.