About one third of the world's population claims to be Christian or follow Jesus Christ. About half of that number claims to be part of the Roman Catholic Church, and the other half is either part of another denomination or no denomination. However, membership in a Christian denonomination or church institution is never required or even mentioned in the Bible. It is not necessarily a bad idea, but it has always been man's idea, not God's idea. Man looks at the outward appearance, but the Lord looks at the heart (1 Sam. 16:7). What is important is for a person to be a member of Jesus' invisible and timeless Church that has no roof or walls. Men who want to control the work of God may claim that their institutions are the same as Jesus' church, but they have no Biblical basis for such claims. The information below can apply to many large denominiations or institutional churches, but special attention is given to the Roman Catholic Church due to it being the largest denomination and having the worst track record of abuse and corruption in all of Church history.
Christianity started after Yahweh Jesus became a Jewish man and started teaching about the Kingdom of God. After He died and was resurrected and ascended to heaven, His disciples carried on His work of teaching, preaching, healing, casting out demons, raising the dead and performing all kinds of miracles. The work started as a Jewish sect but eventually became open to people of all cultures (non-Jews or Gentiles.) It spread rapidly due to the sincere love of early Christians and their willingness to die for the sake of their faith. The sword of true followers of Jesus was the Word of God (Ephesians 6:17), not a physical weapon. Due to it being an exclusive religion (only followers of Jesus are promised eternal life), many people hated Christians and persecuted them. It was actually an illegal religion for hundreds of years until 313AD, when the Roman Emperor Constantine legalized Christianity and merged the Roman church and the Roman state into one entity. Many people believe that this is part of the "mystery" Babylon spoken of in Revelation 17, i.e., it seemed like a good idea but was actually a bad idea, as it merged a spiritual, other-worldly system with a worldly system. Although many good, holy men and women have always been a part of the Roman institutional church, a lot of worldly and even evil men and women have been a part of it too. This has led to many divisions and new denominations, since light and darkness cannot have fellowship (2 Corinthians 6:14-17).
Church history shows that over time most of the denominations have followed the lead of the Roman institutional church and have developed into dead religion that isn't much different from non-Christian religions except that to the extent they use the Bible, they are superior to other religions. The problem is that when people exchange intimacy with their Creator for ritual and boring religion, they tell Him that they prefer to determine what their relationship with Him looks like rather than let Him decide. (Our Creator gave us the Bible through the special inpiration of 40 loyal followers to help us know what He wants in a relationship.) When institutional churches little-by-little drift away from the Bible, eventually the Spirit of God drifts away from them. Of course, our Creator is patient and allows for revival and inner renewal, but historically that only happens on a small local level. In fact, the leadership of most large denominations have been infiltrated to some extent by secret societies and other agents of the devil.
Jesus was silent on institutional churches. He only mentioned the invisible, timeless Church one time (Matthew 16:18) and a local assembly of members of the invisible, timeless Church two times (Matthew 18:17). Instead, He mostly focused on the Kingdom of God, of which He is the King and His followers are citizens. He also taught that unless people are born from above they cannot see or understand the Kingdom of God (John 3:3). Furthermore, He taught that at the end of this age, He will return to judge all individuals and separate his real followers from the fake ones. (See Matthew 13:24-30 and Matthew 25:31-46.) Membership in an institutional church is not mentioned as significant on judgment day - only what we have done, said and thought. Only a personal relationship Jesus Christ can make that possible, as it makes a person a member of Jesus' invisible and timeless church that has no walls.
Sadly, men in local assemblies of Christians have often institutionalized their assemblies. This has led men in power in these institutional churches to often claim exclusive Divine rights for their institutions to interpret Holy Scriptures and judge matters of faith. This has proven to be very effective in exerting power and influence over people, but it is also displeasing to God, because it is misuse of His name (Exodus 20:7). Sadly, most institutional churches have done this, but throughout church history, the Roman Catholic Church has been the ultimate example of tyrrany in this regard. Millions of people have been systematically interrogated, tortured and/or killed as a result of their unwillingness to be members of the Roman institutional church. The word "Catholic" means universal, which implies (wrongly) that the Roman institutional church has exclusive Divine rights to rule over all Christians. "Catholicism" is a term used to describe the teachings and practices of the Roman institutional church. The term "Protestant" means a person or group that protests against the Roman "Catholic" Church and its teachings and practices. This doesn't mean that all Protestants are part of the true invisible, timeless Church of Jesus Christ, but it does mean that they reject the Roman institutional church's claim to having authority over Christianty. It also doesn't mean that none of the members of the Roman institutional church are part of the true invisible, timeless Church of Jesus Christ. Jesus looks at every individual on a case-by-case basis. He is the great fruit inspector (See Matthew 7:13-23.)
Tragically, the Roman Catholic Church has been in error for centuries, having embraced pagan gods and practices, so it is beyond reformation. Over the centuries, in its quest for world domination, it has murdered millions of people, including many Bible-believing followers of Yahweh Jesus. Although it has in recent decades switched to a warm and fuzzy approach to try to bring other Christian denominations back under its umbrella, it has never repented for its previous jackboot tyrannical approach nor for many of its evil practices. In many ways, it is a cult, as it places the teachings of men above the teachings of the Holy Bible. For a good explanation by a former Catholic priest, Bill Schnoebelen, see Catholicism The Church On Haunted Hill. Even more ominous, it appears to be working hard to establish a global religion in which all institutional religions unite to serve a false savior according to local customs and messianic expectations. For more information, see Has the Beast from the Earth Officially Arisen? Over the years, many other problematic denominations have also emerged. Jesus and Lucifer work usually work in parallel - Jesus for truth and life; Lucifer for lies, deception and murder.
God wants a relationship with every person, but Lucifer, aka the devil or Satan, has tricked people into following false gods and man-made religion. Yahweh Jesus not only created the heavens and the earth and all that is seen and unseen, but He wants to talk to you, help you in daily life and help you overcome problems the devil has caused in your life. He died for you and rose from the dead so you could be set free from sin and have a new life. This is the greatest bargain in all of history! To learn more, just read the Gospel of John and find out for yourself. Also, it is a good idea to find individuals who love Jesus, follow the Bible and are more concerned about serving you than building up an institutional church. Jesus said that He will take care of building His Church (Mt. 16:18). He doesn't need men to do that. People who think otherwise usually end up using people. The important thing is to follow Jesus and obey His commands. He said, "My sheep hear my voice, and I know them, and they follow me. And I give them eternal life, and they will never ever be wasted; and no one will snatch them out of my hand." (John 10:27,28 SCS)