Dear Mary:

The Orthodox have valid Sacraments, thus they are a true Church, but not in the fullness of the faith. The Church in the fullness of the faith that Jesus established was the Catholic Church, that is, the Church under the leadership of His Prime Minister. This is proven in Scripture by the following:

(Mathew 16:18-19) And I tell you, you are Peter, and on this rock I will build my church, and the powers of death shall not prevail against it. I will give you the keys of the kingdom of heaven,[h] and whatever you bind on earth shall be bound in heaven, and whatever you loose on earth shall be loosed in heaven.”

Jesus spoke in Aramaic. Thus, he said, "you are Kepha, and on this Kepha I will build my church". This removes any doubt the the Church was built upon Peter.

The fact that Peter was named the first Pope is confirmed definitively by Jesus quoting from Isaiah 22. He gave Peter the "keys to the kingdom." Keys are the symbol of authority.

(Isaiah 22:20-22) 20 In that day I will call my servant Eli′akim the son of Hilki′ah, 21 and I will clothe him with your robe, and will bind your girdle on him, and will commit your authority to his hand; and he shall be a father to the inhabitants of Jerusalem and to the house of Judah. 22 And I will place on his shoulder the key of the house of David; he shall open, and none shall shut; and he shall shut, and none shall open.

In this passage, all theologians agree, that the Scripture is referring to the secession of the office of Prime Minister. Eli′akim is the new Prime Minister replacing the old one. Thus, this office is one of secession.

Every king as his prime minister who is given authority by the king to administer the kingdom in his stead. Here we see that Eli′akim is clothed with the robes of the Prime Minister and given authority. The Prime Minister is the "father" of the house of Judah (foreseeing the Church). The word Pope is the English transliteration of the Greek, patéras or patér. In Latin the word is, pater. In Italian the word is, padre. In English the word is father. Anytime the word "father" is written in Scripture, that is the word Pope (in English transliteration).

Since the word padre is the word for father in Latin languages, such as Italian, every priest is a padre. This is why the Pope is called the Supreme Pontiff (Padre).

Let us go on to verse 22 in which we read that Eli′akim, the new Prime Minister, is given the keys to the Kingdom. These keys shall open or shut and none can prevent it. The keys are the authority delegated by the King to his Prime Minister. 

Since Jesus quoted from these passages when he appointed Peter, this provides proof that Peter was appointed as the Prime Minister of King Jesus.

It was this passage that converted me from a Baptist minister to a Catholic.

Bottomline: The True Church in the Fullness of the Faith, the only Church established by Jesus personally, is the Church under the authority of the Prime Minister (Pope) of King Jesus. That Church the Catholic Church alone.

God Bless,
Bro. Ignatius Mary