Unity

My heart is heavy tonight, troubled by issues that are far beyond my ability to fix. Laying in bed for hours on end these days, I have plenty of time to think and pray. God and I have been talking about a lot of issues and I'm realizing more and more how little I know and understand.
This morning, I was reading through part of the gospel of John, the part right before Jesus was arrested and crucified. He prayed for His disciples and then He prayed for those who would believe in Him through their message. As part of His prayer, in chapter 17, He said:

20“I am praying not only for these disciples but also for all who will ever believe in me through their message. 21 I pray that they will all be one, just as you and I are one—as you are in me, Father, and I am in you. And may they be in us so that the world will believe you sent me.22 “I have given them the glory you gave me, so they may be one as we are one. 23 I am in them and you are in me. May they experience such perfect unity that the world will know that you sent me and that you love them as much as you love me.

I read that and I ached, and ache still, because I know that Christ's followers are anything but unified these days. Why do we argue and dispute and divide ourselves when the desire of the God we serve is clearly that we serve in perfect unity? What is the answer to this problem? How do we, as modern believers, go about fulfilling the desires of our Lord?
In my life, I left a group of believers that I loved with all my heart, in discord and strife. This happened nearly a year ago and while the pain doesn't tear me apart as it used to, the ache never completely leaves, because it was not right for Christ's followers to tear each other apart like that. It just wasn't. And yet I hear stories similar to mine all the time, stories where one or both parties may have been in the wrong and instead of coming together in love and working through it as God intends, we tear each other apart and both parties go separate ways a bleeding, broken mess.
WHAT ARE WE DOING??? Why are we claiming to follow Christ and yet tearing each other apart?? How are we supposed to live in unity as He prayed we would? How do we, as millions of believers with different opinions of what living as Christ intends us to live looks like, live in unity? How do we work through our differences so that, as Christ prayed on that dreadful night, we "may experience such perfect unity that the world will know that you sent me and that you love them as much as you love me."?
The cost of our discord is not small. In fact, our unity is so important that it was one of the last things Jesus prayed about before He was arrested. I'm seeking as an individual to know what that looks like in my life, how I am to live in unity with my brothers and sisters. I'm also praying that we as a Church, as a body of believers, wake up to the damage we are doing through our division and learn what it means to live in unity.