Where to start? First let’s define what Christianity is…
The base of Christianity is defined by doctrines found in the Holy Bible. Is it just a belief in Jesus the Messiah? Well Mormons and even the Devil believe in Christ. So “belief” in Jesus does not make you a “Christian” per se. You must believe the Bible as it is clear that Jesus is God in flesh and the creator of everything.
There is essential doctrine to follow, but I will focus on only a couple for the sake of brevity; The Roman Catholic Church breaks two essential doctrines. 1) They promote Mary and the Saints to a God-like status and that violates the Commandment to have no other Gods before the true and living God. The RCC says Mary is the “Mediatrix” (CCC 969), and that Mary atoned for the sin of man (Fundamentals of Catholic Dogma pg. 213). Also that “Mary is the subject of preaching and worship” (Vatican Council 11, pg. 420)
The RCC scoffs at the Doctrine of Salvation by Grace through Faith alone, “…that all Men may attain Salvation through Faith, Baptism and the Observance of the Commandments” (CCC par. 2068). This is a knock to the scriptures as it is plain that the Bible says that Salvation is not attained by works;
Romans 3: 27-30 27 Where then is boasting? It is excluded. By what kind of law? Of works? No, but by a law of faith. 28 For we maintain that a man is justified by faith apart from works of the Law. 29 Or is God the God of Jews only? Is He not the God of Gentiles also? Yes, of Gentiles also, 30 since indeed God who will justify the circumcised by faith and the uncircumcised through faith is one.
The Roman Catholic Church claims to be Christian? It is verified to be quite the contrary according to their own beliefs and writings! They break the essential doctrines of the Christian Faith!
I pray that the followers of the RCC see the truth in the Holy Bible, not their own Dogma! God Bless!