If one claims to be Christian, he should be part of the Catholic Church

Yes, and they all are indeed based on the teachings of Christ. This statement contradicts itself. They cannot teach something different and be based on the teachings of Christ, this would mean Christ contradicted himself since the churches' teachings are not the same. An example is the teaching of hell. The majority of Christians believe in hell. Jesus taught the existence of hell (Matt. 7:13-14; Matt. 25:25:46; Mark 9:9:47-48) but Unitarians, Jehovah Witnesses, Seventh-Day Adventists, Christian Scientists and Mormons do not believe in the existence of hell and yet they all claim to be following the teachings of Christ. Remember that those teachings are different because they interpret different the same book. Exactly, and that is what I am saying. Sola Scriptura is not the teachings of Christ and is not even a biblical teaching. The teachings cannot be different if they are the teachings of Christ. Christ taught either one or the other so they both cannot be correct. People of different beliefs inside the same religion don't agree, but they all believe they are following the same teachings. The keyword is "believe". Just because they "believe" they are following the same teachings do not mean they are. If one mathematician says 2+2=4 and another says 2+2=5, are they right? Are they both right? No, it is either one or the other. The definition of Christian is about believing one is following the teachings of Jesus Christ. There is no such a thing as a "real Christian" because there is a disagreement. I never said anything of a "real Christian" but of course one who follows the authentic teaching of Christ are indeed the true followers of Christ. This means that Pro already accepted that they can be called Christians. Yes, I agree. I never said non-Catholic Christians are not Christians. The Catechism of the Catholic Church states: The Church knows that she is joined in many ways to the baptized who are honored by the name of Christian, but do not profess the Catholic faith in its entirety or have not preserved unity or communion under the successor of Peter. Those who believe in Christ and have been properly baptized are put in a certain, although imperfect, communion with the Catholic Church. With the Orthodox churches, this communion is so profound that it lacks little to attain the fullness that would permit a common celebration of the Lord’s Eucharist. (CCC 838) And again, this is not about Church, this is not about institutions or be organized, it is about believing that Jesus Christ is the savior and believing that one is following his teachings. Yet if the bible praises the institution (Church) as being the "pillar and foundation of the Truth" then they means it is important. This is incorrect. There is no connection between the definitions and the question. No actually there is. The debate is about why Non-Catholic Christians should be Catholic. This is why in my opening statement, I wanted to clarify what I was supporting before I got into the discussion. The connection is that Christians believe and teach different things but we only have ONE Jesus who taught ONE meaning and established ONE Church, therefore, shouldn't all followers of Jesus wish to discover this Church and be apart of it so that they can be fully united with Christ in His Church? Even if the definition of Christian was about churches, the foundation of the Church means nothing if the Church as it is now it is not like the original. What you are claiming here is that the Catholic Church should not be called a Christian religion because it is not the same as the Church founded by Christ. This is important because we are sure that the Church evolved, it changed with the world. Their beliefs and their traditions are not static.[1][2] You could say that it is because "humans changed it", but then you would concede this argument too because I would be right. The teachings of the Catholic Church have never changed. As you would say, to simply claim that without showing any sources or evidence is irrelevant. Of course certain laws in the Church has changed and practices and some components of the liturgy, but the meanings have not changed and the dogmatic teachings of the Church have not changed. And the last paragraphs are about why the Catholic Church was the first and original, which means nothing to the definition of Christian. The reason the rest of Christians are not following the Catholic Church is because they don't believe they are following the same teachings of the original Church as how it was the first time. They have the right to be called Christians because of the same reason Catholics have the right to be called Christian, they all believe they are following the teachings of Jesus Christ. Yes they may believe that they are following the teachings of Christ but obviously, they all are not. I have never said that they should not be called Christian, I said if they are claim to be Christian, they should be a part of the Catholic Church. The reason is because the Catholic Church is the Church of Christ and every Christians' objective should be to embrace Christ's Church and uphold its teachings.