One day, I was reading John 17 and I saw something different that I hadn't really noticed before. A little added emphasis should help you to see what I saw:
When Jesus had said this, he raised his eyes to heaven and said,
"Father, the hour has come. Give glory to your son, so that your son may glorify you, just as you gave him authority over all people, so that he may give eternal life to all you gave him. Now this is eternal life, that they should know you, the only true God, and the one whom you sent, Jesus Christ. I glorified you on earth by accomplishing the work that you gave me to do. Now glorify me, Father, with you, with the glory that I had with you before the world began.
"I revealed your name to those whom you gave me out of the world. They belonged to you, and you gave them to me, and they have kept your word. Now they know that everything you gave me is from you, because the words you gave to me I have given to them, and they accepted them and truly understood that I came from you, and they have believed that you sent me. I pray for them. I do not pray for the world but for the ones you have given me, because they are yours, and everything of mine is yours and everything of yours is mine, and I have been glorified in them. And now I will no longer be in the world, but they are in the world, while I am coming to you. Holy Father, keep them in your name that you have given me, so that they may be one just as we are. When I was with them I protected them in your name that you gave me, and I guarded them, and none of them was lost except the son of destruction, in order that the scripture might be fulfilled. But now I am coming to you. I speak this in the world so that they may share my joy completely. I gave them your word, and the world hated them, because they do not belong to the world any more than I belong to the world. I do not ask that you take them out of the world but that you keep them from the evil one. They do not belong to the world any more than I belong to the world. Consecrate them in the truth. Your word is
truth. As you sent me into the world, so I sent them into the world. And I consecrate myself for them, so that they also may be consecrated in truth.
"I pray not only for them, but also for those who will believe in me through their word, so that they may all be one, as you, Father, are in me and I in you, that they also may be in us, that the world may believe that you sent me. And I have given them the glory you gave me, so that they may be one, as we are one, I in them and you in me, that they may be brought to perfection as one, that the world may know that you sent me, and that you loved them even as you loved me. Father, they are your gift to me. I wish that where I am they also may be with me, that they may see my glory that you gave me, because you loved me before the foundation of the world. Righteous Father, the world also does not know you, but I know you, and they know that you sent me. I made known to them your name and I will make it known, that the love with which you loved me may be in them and I in them.
In this beautiful passage, Jesus prays repeatedly and at length for the unity of all believers. Not just any kind of unity, but the kind of unity that exists between Himself and the Father. In giving reasons for this unity, there's one reason He mentions twice. Only a single word (in the NAB version) changes in the repetition, "that the world may believe that you sent me" and "that the world may know that you sent me."
I hadn't been a Christian for very long, but I had picked up enough theology to know that God the Son and God the Father (and the Holy Spirit) are about as tight as you can get---so tight that Jesus died at the request of his Father, so tight that Christians still consider themselves monotheists even though there are clearly three persons here. I was familiar with the language, "three persons in one substance," which described the remarkably intense unity of this Trinitarian God.
So, this is the kind of unity that Jesus prayed for all believers. I could handle the fact that this unity wasn't present reality. "We'll get there," I thought. "How could the Father possibly deny the prayer of his Son?" What really troubled me was that disunity, the very opposite of what Jesus prayed for, was upheld as a value by so many believers within and without my faith community. More than once, I encountered so-called "scriptural arguments for denominationalism!" and romantic portraits of the schisms of the Protestant Reformation.
My troubles were compounded by Jesus' stated intent for the unity. Yes, so that the Church will be "brought to perfection as one," but twice he mentions that His purpose for Christian unity is for people who are not already Christians. The unseen casualties of our present dereliction of duty will be those who don't already believe.
Christian Unity became a priority for me in that moment. I was suddenly aware of the interconnectedness of my own faith journey and the faith journey of others. I resolved not to be part of the problem and to seek ways to be part of the solution, and there was at least one Christian community out there that took unity seriously. I was conscience-bound to take the Catholic Church seriously and to learn more about her.