How do these verses fall short of establishing that? They tell us that not everything about God has been written down.
Yeah. So?
Are we going to get some really good reasons that an argument from silence is somehow going to change anything?
“How do these verses fall short of establishing that? They tell us that not everything about God has been written down.”
That not everything is written down is not equal to knowing what those things are. We do not know. There is no record that can be traced to the time of the Apostles.
The Apostle John’s point in closing his Gospel is that His is a faithful account of the life and message of Christ - despite not being able to include in one book everything Christ did and said. It would be impossible. Despite that reality, his is a faithful account.
He does not say this is a blank check verse that gives justification to believe and teach anything else other than what is written - as equal to what the Spirit inspired.
In fact, at the end of his life, in I John 5:11-13, he concludes with this:
“11 And this is the testimony: God has given us eternal life, and this life is in his Son.
12 Whoever has the Son has life; whoever does not have the Son of God does not have life.
13 I write these things to you who believe in the name of the Son of God so that you may know that you have eternal life
Everything for salvation is in Christ. If you have Him, you have eternal life. If you do not have Him, you do not have eternal life.
And how do you “get” Him?
Not by eating, but John says by believing - entrusting yourself fully to Him.
The Holy Spirit inspired each Word of Scripture. He chose who and what was recorded that we might know Him. There is no evidence anywhere that anything we need for salvation or Christian growth is left out of the Scriptures.
Any claim that this verse or the others quoted are a blank check, is false. You have the testimony of the Apostle John that what a God gave us in a Scripture is enough to tell you how to have salvation.
The remaining question is, do you have salvation now? Have you entrusted yourself to Him fully, as John wrote?
If you do not know for sure, you can know now.