If as Protestant doctrine has it the Christian faith consists of only what is contained in Scripture. Then one would expect that somewhere in the New Testament a statement of this doctrine could be found. Since it is not, than it is no better founded than the “extrabiblical” doctrines that you deplore.
If by "faith", you mean a system of beliefs, then you are off base about what Christians consider faith to be.
My faith is in God. It is trusting in Him.
Hebrews 11:1 Now faith is the assurance of things hoped for, the conviction of things not seen.
John himself says that what he wrote is enough to bring someone to salvation. It's all about Jesus, not having your doctrinal ducks lined up in a row.
The gospel message is a simple one. Repent and believe.
Acts 16:29-34 29 And the jailer called for lights and rushed in, and trembling with fear he fell down before Paul and Silas. 30 Then he brought them out and said, “Sirs, what must I do to be saved?” 31 And they said, “Believe in the Lord Jesus, and you will be saved, you and your household.” 32 And they spoke the word of the Lord to him and to all who were in his house. 33 And he took them the same hour of the night and washed their wounds; and he was baptized at once, he and all his family. 34 Then he brought them up into his house and set food before them. And he rejoiced along with his entire household that he had believed in God.
Acts 17:30-31 The times of ignorance God overlooked, but now he commands all people everywhere to repent, because he has fixed a day on which he will judge the world in righteousness by a man whom he has appointed; and of this he has given assurance to all by raising him from the dead.”
Romans 10:9-13 ...... because, if you confess with your mouth that Jesus is Lord and believe in your heart that God raised him from the dead, you will be saved. For with the heart one believes and is justified, and with the mouth one confesses and is saved. For the Scripture says, “Everyone who believes in him will not be put to shame.” For there is no distinction between Jew and Greek; for the same Lord is Lord of all, bestowing his riches on all who call on him. For “everyone who calls on the name of the Lord will be saved.”
Too many denominations make salvation way too complicated.
The Law was put in charge to lead us to Christ. It's by HIM we are saved. And actually, even the OT alone is enough to bring someone to Christ to be saved.
John 5:39-40 You search the Scriptures because you think that in them you have eternal life; and it is they that bear witness about me, yet you refuse to come to me that you may have life.
“If as Protestant doctrine has it the Christian faith consists of only what is contained in Scripture. Then one would expect that somewhere in the New Testament a statement of this doctrine could be found. Since it is not, than it is no better founded than the “extrabiblical” doctrines that you deplore.”
What??!!
Why don’t you put that in English instead of some Catholic gibberish?