"All SCRIPTURE is given by inspiration of God, and is profitable for doctrine, for reproof, for correction, for instruction in righteousness: That the man of God may be perfect, thoroughly furnished unto all good works." 2 Tim. 3:16,17.
Want doctrine? Read Scripture. Want to find true correction? See Bible. Want to know what God's righteousness for man is? Refer to God's Word. Want to be perfect in God's eyes, completely and thoroughly furnished to be His workman? God's Word will THOROUGHLY furnish you.
I didn't say it. HE did. That's His promise. That Scripture is ALL we need.
It doesn’t say only in there anywheres.