Because this Gospel that was preached was the “source of all saving truth and moral discipline” Jesus said that Salvation comes from believing the Gospel the apostles preached.
In Mark 16:16 He said to them, "Go into the whole world and proclaim the gospel to every creature. Whoever believes and is baptized will be saved; whoever does not believe will be condemned.”
Jesus never said salvation comes from believing the Gospels they wrote, or from believing scripture or from believing the bible.
Jesus said salvation comes from believing the Gospel they taught, that is, the one handed down in Tradition, the Word of God handed down in Tradition. Thus salvation comes from believing the Word of God, or Sacred Tradition that apostles handed down orally and by example.
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Later on the Holy Spirit moved some apostles and apostolic men to write the narratives of the life of Jesus, the four Gospels. “The sacred authors, in writing the four Gospels, selected certain of the many elements which had been handed on...”[1](http://forums.catholic-questions.org/#sdfootnote1sym)
These narratives of the life of Jesus are also called “Gospels” because they contain certain of the many elements of the “full and living Gospel” as the direct words of Jesus about the good news of salvation. Thus they are also the Word of God.
But, There is not a single book of the Bible, not a single chapter of the Bible that claims to be a summary of this Gospel that the apostles taught and preached.
And this Gospel they taught and preached was so extensive, that the apostles could not remember it all. Jesus had to send the Holy Spirit so they could remember all He taught them.
Now the apostles could not proclaim the Gospel by reading scripture because nowhere does the bible claim to present the Gospel the apostles taught and preached. The bible claims to present narratives of the life of Jesus and salvation history, not the Gospel the apostles taught and preached. No one can learn the Gospel the apostles taught and preached by reading the word of God in the form of salvation history.
Even Martin Luther, the greatest promoter of “Scripture alone” could not teach his doctrines by scripture alone. He had to write two catechisms, one for children, the Small Catechism and one for adults, the Large Catechism, which he said was a “Short Summary and, Epitome of the Entire Holy Scriptures.”
So how did the apostles teach their Gospel? What was the content of this Gospel? We know from the teachings of the early Church that first they had to teach who God was, why He created us and why He sent His son Jesus. If a person wanted to learn more and was interested in becoming a Christian and being freed from the slavery of sin, then he would be taught the Trinity, salvation history (scripture), then the articles of the Creed, Sacraments, Commandments and prayer. In other words, the apostles had to organize all they had learned directly from Jesus and the Holy Spirit and put it in a form that people could remember and understand. If we notice Catholic Catechisms today, starting with St. Augustine’s and continuing with many others, especially the two official Catholic Catechisms, the Roman Catechism, and the Catechism of the Catholic Church, they are in the form of the creed, sacraments, commandments and prayer. Why? Because this is the form and method the apostles handed down when they taught the Gospel. Remember, the apostles did NOT learn the Gospel by reading the bible. They were taught “everything” and “all things” directly by God. And neither do the written Gospels claim to present the Gospel the apostles taught and preached. They claim to be narratives of the life of Jesus. Thus the Gospels that were written and the Gospel the apostles taught and preached were distinct. The Gospels were salvation history of the narratives of the life of Jesus, with some doctrines also present, while the Gospel the apostles proclaimed were all the teachings of Jesus and the Holy Spirit, all the ways of worship they learned from Jesus and His doctrines presented in the form of the creed, sacraments, commandments and prayer. This Gospel was simply the whole Catholic faith, centered around the Good News that God, out of love for us, sent His son Jesus to free us from the slavery of sin so we can live in union with Him now and forever. So the Catholic faith and the teachings of the Catholic faith do not originate with scripture, but were taught to the Church directly by God and the Holy Spirit. The catechisms of the Catholic Church are do NOT originate from the teachings of scripture, as Luther’s catechisms claim to do. Catholic catechisms are simply a summary of the Gospel the apostles proclaimed. That is why the Church teaches,
“Catechesis is nothing other than the process of transmitting the Gospel, as the Christian community has received it, understands it, celebrates it, lives it and communicates it in many ways.”
General Directory for Catechesis 105
and
“In local catechisms, the Church communicates the Gospel in a manner accessible to the human person so that it may be really perceived as the “Good News” of salvation”
General Directory for Catechesis
Now, since the teachings of the Catholic Church do not originate with scripture, but come directly from the Gospel that Jesus and the Holy Spirit taught directly to the Church, and since the bible does NOT claim to present this Gospel anywhere, other than certain elements of this Gospel found in scripture, there is no reason that any doctrine of the Catholic Church HAS to be found in the bible, other than a few elements that come alone with salvation history. There is certainly no reason all doctrines must be found in scripture. If scripture claimed to present the Gospel the apostles taught and preached, then we would have a basis for that claim. But scripture only claims to present salvation history and some of the teachings of Jesus. Now, the Church does claim to present this living Gospel the apostles handed down to her. Thus, the Catechisms of the Catholic Church do claim to be “a significant contemporary expression of the living Tradition of the Church.” The same Tradition the apostles learned from Jesus and handed down as the Gospel.
The same Word of God the apostles handed down to their successors, the Pope and bishops of the Catholic Church. The same Word of God through which Jesus says we are saved. So it is only in the Catechisms in which we would expect to find almost all the teachings of God , NOT the bible.
