Jesus prayed these words before going to the cross. He was praying for the subsequent generations of believers that would follow in the centuries ahead. Note how he explicitly links Christian unity with people believing in him. There is power in believers coming together in worship and in service. Unity is itself a witness to the truth of Jesus Christ.

I pray not only for these, but also for those who believe in me through their word. May they all be one, as you, Father, are in me and I am in you. May they also be in us, so that the world may believe you sent me. I have given them the glory you have given me, so that they may be one as we are one. I am in them and you are in me, so that they may be made completely one, that the world may know you have sent me and have loved them as you have loved me. Father, I want those you have given me to be with me where I am, so that they will see my glory, which you have given me because you loved me before the world’s foundation. Righteous Father, the world has not known you. However, I have known you, and they have known that you sent me. I made your name known to them and will continue to make it known, so that the love you have loved me with may be in them and I may be in them.

John 17:20-26 CSB