The supposed distinction between the visible, divided church and the invisible, united church that allows Protestant theology to escape the implications of Jesus's high priestly prayer in John 17 may be rooted in the first lie recorded in the Bible: "You will not surely die [if you eat the fruit]."
At first, Satan seems to have told the truth. In fact, Adam and Eve did not die (at least immediately) in the physical sense. But we know that they died spiritually the moment they touched the forbidden fruit.
Satan's deceit takes advantage of an apparent separation between our physical and spiritual states. Yet, Satan indeed was proven the ultimate liar, since Adam and Eve died countless deaths each day of their remaining lives, culminating in their final deaths, neither of which were part of God's original "plan" (though God's foreknowledge of the fall of both angels and men can not be denied). Further, Eden could only be reentered by the sword. In every respect, the realities of spiritual and physical death were very much intertwined for Adam and Eve.
I think that recent Protestant theology relies upon and reinscribes the supposed division between the visible and invisible that was the unspoken premise in Satan's first lie to man. (I say recent, since it is my understanding that the original "reformers" disagreed with each other over essential doctrines so vehemently that they thought each other to be the offspring of Satan himself, not fellow brothers united in a spiritual way. I think the "spiritualization" of the church is symptomatic of modern Christians' profound misunderstanding and even distrust of doctrine.)
Except now Satan's lie is reversed: If you eat the fruit [dividing the visible church into countless denominations and non-denominations], you [the invisible church] will not die. Unlike Adam and Eve who died a spiritual death that manifest itself physically, we accept a physical death (visible division) on the premise that it does not divide us spiritually. Love can not tolerate these divisions! Christians need to reunite so that Satan's lies can be thoroughly routed from the church!
Here are some questions that I hope non-Catholics consider in prayer:
1. Does the current, splintered state of Protestantism reflect the type of unity that Jesus prayed for in John 17?
2. What doctrines must be believed for someone to be considered a member of the invisibly united church? Who decides, and on what authority?
3. Apart from the doctrines listed in response to the second question, how many doctrinal divisions and clearly false doctrines does it take for a person to be considered NOT part of the true invisibly united church? Are Mormons part of the true invisibly united church? Can one be only partially united to the true invisibly united church?
4. Where does the Bible say that it is acceptable for Christians to believe wildly different doctrines, as long as they agree on the "essentials" [please refer to the answer given in the second question for what these essentials might be]?
5. Where do the earliest fathers of the church (Peter, Paul, John, Ignatius, Clement, Polycarp, Justin, etc.) say that it is acceptable for Christians to believe wildly different doctrines, as long as they agree on the "essentials"?
6. Do Jesus and the Father disagree on any doctrines? If yes, which ones? If no, is their agreement essential or unessential to their Triniterian unity?
7. Jesus prayed that Christians would be one like He and the Father are one. Did Jesus qualify this statement to exclude doctrinal oneness? Was Jesus simply being naive about the possibility of Christian doctrinal unity, or do you think he had a plan in mind for how such unity might be achieved? Do we feel naive when/if we hope, pray, and work for complete Christian unity? Do others treat us as being naive? Was Christ's prayer naive?
8. Was such a unity ever present within Christianity from the first century to the present day? If so, how was it maintained?
9. "You are the light of the world. A city on a hill cannot be hidden." (Matthew 5:14) How can the true church be a light to the world if it is strictly an invisible entity?
10. "May they be brought to complete unity to let the world know that you sent me and have loved them even as you have loved me." (John 17:33) How will the world be convinced by a complete unity if all they see is complete disunity? How does "complete unity" exclude doctrinal unity? How can the world see anything that is invisible?
11. How can an invisible church be the "pillar and foundation of the truth" (1 Tim. 3:15) if the visible members that make up this church disagree on almost every doctrinal truth-claim? Also, why does the Bible teach that the church is the pillar of the truth when Protestants teach that the Bible is the pillar of the truth (if not exactly in those terms)?
12. If a brother sins against me (say, by accusing me of heresy) and the situation can not be resolved, Jesus says I should take the matter to the church, and if my brother doesn't listen to the church, he should then be treated "as a pagan or tax-collector." (Matthew 18:15-17) Jesus then immediately reminds the apostles that "I tell you the truth, whatever you bind on earth will be bound in heaven, and whatever you loose on earth will be loosed in heaven." (v. 18; see also Matthew 16:19 and Isaiah 22:20-24) How does Jesus's teaching about the church in Matthew 18 make sense if the church is a visibly-divided invisibly-united entity with no authority? Did Jesus establish a retirement clause for this and other versus that suggest apostolic authority? Did Matthias have the same authority as the apostles when he assumed the bishopric vacated by Judas in Acts 1:20-25? Did the early church treat the successors of the apostles as having the same authority to bind and loose as the early occupants of the cathedra?
13. Could it be that the notion of the invisible unity of all believers is an idea created within Protestant theology to ignore the splintering of Protestantism that has been present since the first "reformers" broke away from the true church?
14. As a thought experiment, consider for a moment the alternative notion from the Protestant one. Consider that the visible splintering within Christianity is symptomatic of real spiritual separation within the Bride of Christ. Consider that Christ was not being naive in offering his prayer in John 17. Consider that no one until the sixteenth century honestly questioned what the "true church" was. Consider that all the fathers of the early church saw unity as something that existed through the authoritative heiarchy of bishops in union with the bishop of Rome and all those faithful who remain obedient to their teachings. Consider that the Holy Spirit is actually 100% successful in bringing about Christian unity by guiding all Christians who obey the church through whom he speaks to complete doctinal and moral unity. In contrast, consider the doctrinal disunity and denominationalism wrought by the doctrine of Sola Scriptura. If you can acknowledge that Sola Scriptura (historically) leads only to disunity but an authoritative magisterium leads (historically) to unity, but you reject the latter option, how else might Jesus have expected His prayer for complete unity to be answered?
15. Is Jesus's prayer for unity being answered today? If no, consider that "the prayer of a righteous man avails much." (James 5:16) Jesus is the most righteous man that ever lived. Why is His prayer for complete unity not being realized today? Was it ever realized?
16. Can the model of authority based on the Bible Alone that is the foundation for Protestant theology be expected to lead to Christian unity? Who has the authority today to interpret the Scriptures in a way that must be believed with the obedience of faith?
May we all be one as Jesus and the Father are one. Lord, pour out your Spirit like never before, and give us hearts and minds open to the truth of your Church. Amen!