The book has not always existed. The Church is older than the Bible. If one is not saved through the Church - than the Bible cannot save anyone. The bible derives it’s authority from the Church not the other way around.
Then why do Catholics quote Scripture to give the Church and Peter their authority? You can't have it both ways. That which is of lessor authority cannot impart greater authority to someone or something else.
If the Catholic church is what gives Scripture its authority, then it cannot legitimately use Scripture to validate its teachings.
The RCC should then, at that point, at least have the integrity to admit that their claims to authority as simply based on their say so.
“Then why do Catholics quote Scripture to give the Church and Peter their authority?”
Catholics quote scripture to prove that Jesus Christ gave St. Peter this authority and founded his Church.
Again - it is not the bible that grants them this authority, but Christ himself. The bible - as an accurate testimony of Christ’s teachings serves as our witness to Christ’s mission on earth. Part of which includes the disciples and the founding the Church with the Apostles, Pentecost, and the coming of the Holy Spirit in Acts, etc.
Again, all these things happened before even the first Gospel was written.