[papertyger]

The Triune nature of God is taught in Scripture. It is a systematic teaching of the totality of what Scripture reveals about the nature of God.

How is that statement credible when Trinitarian theology predates the codification of Scripture?

[aMorePerfectUnion]

"How is that statement credible when Trinitarian theology predates the codification of Scripture?"

Understanding the teaching of the Apostles through circulating letters laid out the Triune Nature of God.

When the church was attacked from within, it was formally laid out to guard against encroaching heresy.

[daniel1212]

The Triune nature of God is taught in Scripture. It is a systematic teaching of the totality of what Scripture reveals about the nature of God.

How is that statement credible when Trinitarian theology predates the codification of Scripture?

How is that statement credible when men such as Apollos "mightily convinced the Jews, and that publickly, shewing by the scriptures that Jesus was Christ," (Acts 18:28) although that also predated the complete codification of Scripture.

Is your argument that a complete infallible canon is essential in order for the veracity of a doctrine to be based on Scriptural substantiation in word and in power, under SS?