One in Christ?

In John chapter 21 Jesus is praying for his disciples and in verses 20 & 21 he says, "Neither pray I for these alone, but for them also which shall believe on me through their word. That they all may be one as thou, Father, art in me, and I in thee, that they also may be one in us: that the world may believe that thou hast sent me." I wonder how this is working in the body of Christ. We should all be one in Christ and not divided over man made religious rules that seem mostly rooted in touch nots and taste nots. I recently heard of a minister that was telling Christians that they are going to hell for not following the dietary laws of the Old Testament. Are we loving our brothers and sisters in the Lord the same way we love ourselves? Can we fellowship with all those who are born again? If not, why not? What do you suppose those in the world are thinking as they view the Body of Christ in such an anemic condition?