“Being one with Christ, you are one with His people; but when you are looking for this unity, look not for an outward but for an inward thing. Do not look for a matter that is to be written on sheets of paper, on rolls and books, but look for a bond written on hearts and consciences and souls. Look for a spiritual union and you will find it. If you look for the other thing you will not find it, and if you did find it, it would be a great and awful thing, from which you might pray God to deliver His Church.”
Charles Haddon Spurgeon commentary on John 17:20-21, as quoted in Are We Reformed? by Dr. George Ella.
20 “I do not ask for these only, but also for those who will believe in me through their word,
21 that they may all be one, just as you, Father, are in me, and I in you, that they also may be in us, so that the world may believe that you have sent me. ESV
This isn’t talking about there not being any outward evidence of Salvation. What it is discussing is the outward jumping through the “right” hoops in the “right” order. Such as:
~ Using the “right” Bible Translation.
~ Being Baptized by the “right” Individuals.
~ Being a member of the “right” and only acceptable church denomination.
~ Performing the Lord’s Supper in the “right” way.
The things that would be found in your “church letter” or “church’s roll”.