Then we would have to start doubting scripture though which doesn’t seem like a good ideer
“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, throughly furnished unto all good works.”
2 Timothy 3:16-17 KJV
air we begin doubting that it’s authentic of sayong it’s corrupted our trust flies out the window of all the information God has made known to save us . And then everyone is left to think what they think and claim it’s gods spirit telling them
Is god capable of protecting the integrity of his word tbat he said would be preached to all creation ? I believe he is and so we can trust the scriptures without that trust we’re going to end up being “our own Bible “
“We have also a more sure word of prophecy; whereunto ye do well that ye take heed, as unto a light that shineth in a dark place, until the day dawn, and the day star arise in your hearts: knowing this first, that no prophecy of the scripture is of any private interpretation. For the prophecy came not in old time by the will of man: but holy men of God spake as they were moved by the Holy Ghost.”
2 Peter 1:19-21 KJV
Also, in your quoted verse, it is the "doctrine, for reproof, for correction, for instruction in righteousness" that completes a believer. Someone else, other than the one being instructed, is actually doing the instructing, reproofing, correcting, etc. Otherwise we would be left to read and interpret the scriptures for ourselves: starting as babies, we would say it means whatever we want it to say. Eventually, heaven forbid, we would have churches supporting sin as a lifestyle, preachers robbing the flock, and a cult of personality behind the pulpit.
Wait. What?!