Jesus divides the saved from the unsaved. He prayed the Church be One in John 17 and Paul admonished the Church to be One in 1 Corinthians 1, and we are!!
What you appear to misunderstand is that the invisible church has and always will be one in Christ, but the “churches” of men are not the church. They are at war with the church, and the one that is most at war is the Roman ‘catholic’ church.
.