Brother, pause to thank God for putting this question in your heart! And not only that, for leading you to passages that directly address the question. In the old testament, the Jews fragmented into several groups, one of which was the Samaritans. The doctrinal differences between the Samaritans and the Jews were relatively small, yet the Samaritans were despised by the Jews as being outside the covenant. Christ used this ungodly attitude on the part of the Jews to humble them with his stories of good Samaritans, showing that God recognized the good deeds of those who were outside the covenant.
NEVERTHELESS, Christ proceeds to tell Photini (the name of the Samaritan woman at the well is, by oral tradition, Photini or Photina, the name given to her at baptism by the Apostles) that the Samaritans are in error! He does so very lovingly, obviously, but his admonition is clear: salvation is of the Jews.
The body of Christ is not 30,000. It is one. So, why do we have so many groups claiming to be the body of Christ? The direct answer is heresy. This is a word Christians do not like to confront, mainly because of its association with the Inquisition. But it is not only not a word we should fear, but one we should study. Heresy means literally, "choice." Heretic means, "chooser." Those who espouse heresy are, then, those who choose to believe something other than what has been handed down--something other than the gospel "once delivered unto the saints."
Heresy was clearly of great importance to both Christ and the Apostles. St. Paul includes heresy as one of the works of the flesh in the list he gives in his letter to the Galatians: "Now the works of the flesh are manifest, which are these; Adultery, fornication, uncleanness, lasciviousness, idolatry, witchcraft, hatred, variance, emulations, wrath, strife, seditions, heresies, envyings, murders, drunkenness, revelings, and such like: of which I tell you before, as I have also told you in time past, that they which do such things shall not inherit the kingdom of God." Today, we avoid the topic of heresy altogether, but the Apostle places it in a list filled with sins that would make us all blush!
St. Paul also gives us a reason for why heresy is allowed by God to attack the church: "For there must be also heresies among you, that they which are approved may be made manifest among you." Heresy helps refine our expression of what we believe. But we never change what we believe. "Jesus Christ is the same yesterday, today, and forever." And in Malachi, a similar sentiment is expressed by God: "I am the Lord your God...I do not change."
Christ himself says that not one jot or tittle will be ignored by God. The word he actually uses is "iota", which refers to a tiny, seemingly insignificant subscript in the Greek language.
Furthermore, Christ has this to say regarding his church: "And on this rock [petra--not Petros] I will build my Church, and the gates of hades shall not prevail against it." That is to say, Christ will build his church on confession of faith, such as that made by the Apostle Peter, and the gates of hades shall not prevail against it.
Most churches today are, for all their good intentions, founded on the principle of restoration. The grand claim is that the church erred at some point, or fell away from the true faith, and that there was nobody left to continue the faith. Therefore, it must be restored. It's hard to blame anyone for this falsehood, since the Prophet Elijah himself fell into it. But God answered him, "I have preserved 7,000 in Israel that have not bowed the knee to Baal." We see in the scriptures something that contradicts the idea that the church falters completely. We see first of all the continuity to which God refers. We are reminded that the church is the Body of Christ. While some may fall away from the church or even mislead others in the church, the church itself does not falter. To say that it falters is to say that Christ himself falters, or that he lied to us regarding the triumph of his church. It would be to admit that the gates of hades had indeed somehow prevailed against God.
I realize that my answer is not one that Christians would like to hear. For many, it is enough to confess the name of Jesus Christ. You can see this yourself from the answers you have already received. But we learn from the Acts of the Apostles that those who tried to cast out demons in the name of Christ without reception into his church were unsuccessful. As hard a saying as this is, the jots and the tittles clearly do matter. These are not my words, brother: they are written in the Gospel. They may not be verses that are often marked with highlighter, but they are there.
At the outset, it also appears divisive. It's as if in the claim that, by the scriptures, there can be only one, true church, there is an attack made on those of all other groups. But isn't it strange? These groups splintered over time from the church itself or from another splinter. Is it not these groups that are the divisive ones? Still, an appeal to unity--to the idea that the church must be one, was always one, still is one, and will always be one--is very often met with scorn or derision.
But this nevertheless brings us to a very important question: if such a church exists, where is this group, this remnant that God has preserved throughout history? On this forum, I will not presume to answer this question for you. God is clearly leading you to seek out this answer, and I believe he will continue to lead you to the answer. But make no mistake: there is only one Body of Christ.
It reminds me very much of the scene in the third Indiana Jones movie (oh, I hate to appeal to a movie, but the scene illustrates it so well). Indiana Jones must choose the correct holy grail in a room full of grails. Which one is it? Rather than being lured by the splendor and beauty of the golden chalices in the room, he thinks carefully: "Jesus was a carpenter." After some searching, he quickly locates a modest wooden goblet, and of course, he is correct.
I hope you will take a similar historical approach. I hope you will start with those churches that can demonstrate a clear lineage (and by clear lineage, I mean they have the names, dates, and documents to back up their claims) to apostolic succession (there are less than ten, so this will narrow your search quite quickly). I hope too that you will include your wife in this search. This will not be so easy an answer to find as Indiana Jones, but I know you must want to do it. You would not have asked the question otherwise, and you would have been satisfied already by the answers you have been given. But it seems by your replies that you are not quite satisfied--at least not yet.
Brother! In some ways, I envy you, because the journey you are about to begin--the deep, historical search you will undertake--is a great, enriching experience. Christianity will mean so much more to you, more than it ever has. May God send his grace to enlighten and lead you.