It's interesting how many people think it is their job (or your job or mine) to fulfill Jesus' prayer. I'll have to admit to being deficient in the requisite power to fulfill his request, but that's why he addressed it to God, not to the believers. In the foregoing night of teaching he commanded the disciples to "love one another" (John 13:34, 15:17) but didn't command them to "be one" because only God has the capacity to make them/us one. It is "by one Spirit we are all baptized into one body" (1 Cor 12:13), not a human act, but an act of God. As part of the body believers have responsibilities of behavior toward one another that are not divisive, but the direction for unity for believers is to keep what the Spirit has produced, not produce it ourselves. It is kept through right attitudes, not through compromise on God or Christ or baptism or authority or anything else the scriptures teach.

When Jesus prayed for "complete unity" in John 17:23 it is prefaced with the words "brought to" which is to say, it is a process, growing toward what God wants us to be, increasingly reflecting the glory of God and the presence of Christ in the Christian. The same concept is stressed in Ephesians 4:11-16, unity is a product of God working in each believer toward perfection as believers do the work of God. The kind of unity Jesus was praying for and Paul was teaching about can't be produced by human decision or compromise, but only by learning to be like God. Again, as Paul described, that calls for a pure church with godly leaders, faithfully building each other up in love, so that God's power and glory, as prayed for by Jesus, can bring them to unity. Unity is the finished work of God in the believers, not the job of the church. But making unity among churches a human goal has always resulted in movements that neither glorify God nor obey Jesus' commands, which he also stressed as necessary on the night of his betrayal.

John 14:15 "If you love me, you will obey what I command. (NIV)