First off they did not start out Christianity. Roman Catholicism as we know it today came some 600 years after Christ. You need to read the early church fathers, Tertulian, Clement of Alexandria and Augustine of Hippo.
As to Roman Catholics being Christian, the answer is yes they can be. While they bring a great deal of heretical baggage with them the central tenets of the faith reside in the structure of their beliefs.
1. Salvation is by grace through faith and not by works.
2. A belief in the Trinitarian concept of God; Father, Son and Holy Spirit. One in essence yet separate in entity. Co-eternal and equal in nature and substance.
3. Proclaiming Jesus as Lord and Savior with ones mouth and believing in Him as having risen from the dead.
4. Accepting the Scriptures as the inspired word of God.
I expect to find Roman Catholics in heaven just as I would find Protestants. The same applies to hell as well! Matt 7:21"Not everyone who says to Me, 'Lord, Lord,' will enter the kingdom of heaven, but he who does the will of My Father who is in heaven will enter. It is not up to me to determine who gets in or not just so long as I make the grade. You know pass go collect $200, free pass to eternity in Heaven!
Yes Yichel, we are indeed Christians. . . in the truest sense of the word. Our Religion dates back to Christ himself. He placed his teachings in the hands of his deciples and told them to carry on his works. The Holy Spirit decended on them at Pentecost and we believe that the Holy Spirit has been leading us since then.
