Jesus' prayer for us: Unity in the church

“My prayer is not for them alone. I pray also for those who will believe in Me through their message, that all of them may be one, Father, just as You are in Me and I am in You. May they also be in Us so that the world may believe that You have sent Me.” John 17:20-21
John 17 contains a unique insight: we see Jesus praying directly to His Father. First, He prays concerning Himself, stating that He has finished the work He was given to do. Then, He prays for His disciples, for their protection. Finally, He prays for us. That’s right: “for those who will believe in Me through [the disciples’] message”. Once we get over the shock of discovering that Jesus actually prayed for us, we note specifically what He was asking for: unity amongst us, in love. “May they be brought to complete unity to let the world know that You sent Me and have loved them even as You have loved Me” (John 17:23).
I wonder what Jesus thinks when He sees the competition and conflict between the various denominations in the church today, the teaching from certain pulpits that ‘if you don’t belong to our church you aren’t saved’. And have you noticed how unbelievers will point to this division and mock Christianity, saying, ‘Which one’s right?’ People will even ask you, ‘Which religion are you – Baptist? Methodist? Lutheran?’
It all starts with us. What is our attitude towards Christians who choose to fellowship in a different denomination than us? Do we look down on them, or do we welcome them with open arms, as the brother or sister they truly are? I understand that different ‘flavours’ of churches appeal to different people, at different stages in life. One church is unlikely to meet the needs of all people (especially when different cultures and languages are factored in). But we shouldn’t be saying ‘I’m a Methodist’ or ‘I’m a Baptist’ at the expense of saying ‘I’m a Christian’.