Originally Posted by Megenoita
The name "Christian" derives from being a follower of Christ. Studying His life, death, resurrection and teachings, and following Him, is what makes one a Christian.
The problem with, say, Mormons, is that they say Jesus is "a god", but not one with God the Father. Jesus says in John 8, "Unless you believe that I AM (title for God the Father), you will die in your sins." Jesus was putting His deity as a central part to believing in the true God.
Jehovah's Witnesses also deny that Jesus = God.
Catholics, if they hold to their own doctrine (many do not), believe many anti-Scriptural views, the most important probably being that they believe the way to bridge the gap in the relationship with man and God is through man's own works--baptism as a baby, confirmation, doing good deeds, tithing, church attendance, etc. The Bible clearly teaches a salvation that is by faith without works. Jesus fought the Pharisees who had a similar view as Catholics.
Catholics also teach that the Pope speaks "ex cathedra" and his words are on par with Scripture, as well as traditions of the Catholic Church--this means they can make new rules as they see fit and deceive the people into thinking it's from God. But Jesus Himself said He did not come to add or take away from the Law, but to fulfill it. He quoted Scripture when tempted, for every answer to the temptations. Catholicism has become a political power from their corruption.
Catholics teach that priests mediate between God and man, but the Bible says "There is ONE mediator between God and men, the man Christ Jesus". Therefore we are to pray to God through Christ, not speak to a priest as if he's some special person.
The Bible says "Call no one on earth, father", referring to a reverential, spiritual name. This is what priests' title is, "Father Joseph", or w/e.
One of the most important teachings Catholics have that separates them from Christ's teachings is in forbidding marriage. The Bible says in later days there will be deceivers who teach bad doctrine, one of which is "forbidding to marry". In light of context, it is not a prediction of the Catholic Church but it does demonstrate that men with urgings are supposed to marry. Another passage says "It is better to marry than to burn with passion".
I could go on and on--basically if someone is a certain denomination, that means nothing, because you never know what they really believe. I've met Catholics who love God and don't know what the Church teaches. I've met Baptists (supposed to be really good theologically) who are certainly not followers of Christ. It doesn't boil down to a name or denomination, it boils down to the heart, whether a person believes the Bible's teachings concerning the Christ, believing the gospel--that Christ died for our sins and was buried, raised, and witnessed, and ascended to the Father.
If you are an atheist or unbeliever and want to know if someone is a Christian, without knowing the Bible's teaching yourself, it's going to be hard to sift through the rubbish. I mean, most genuine Christians don't even know well enough to tell if certain people are professing the truth or not. It's not always easy, and of course we never know the heart. But if someone says they are a Christian and then believe against the teachings of the Bible, they may or may not be one, but where they go astray, they are not repping the biblical Christian faith.
This is why when I read these forums and people give their religious experiences and why they disbelieve, although I'm a Christian, I agree with their sentiments--given their experience with "religion", I would feel the same way. They swing the pendulum and renounce all religion, when really although they should abandon the caricature of religion they've experienced, they should not go to the opposite end of the spectrum; they should seek the truth wherever it is, even if it's still in the realm of "religion". True Christianity is much different than what almost any unbeliever pictures, therefore they are not even disbelieving in Christianity so much as the caricature they've judged as such.