But does that mean God didn't't say it? What logic is there in trusting only God's written word and not his other teachings?
Christians only believe was has been written in the Word of God. Anything else you are only outside of the truth.
ROM 4:3=
For what does the Scripture say? "And Abraham believed God, and it was reckoned to him as righteousness."
ROM 10:11=
For the Scripture says, "Whoever believes in Him will not be disappointed."
GAL 4:30=
But what does the Scripture say? "Cast out the bondwoman and her son, For the son of the bondwoman shall not be an heir with the son of the free woman."
MAT 22:29= But Jesus answered and said to them, "You are mistaken,
not understanding the Scriptures, or the power of God.
LUK 24:27= And beginning with Moses and with all the prophets, He explained to them the things concerning Himself in
all the Scriptures.
JOH 5:39 "
You search the Scriptures, because you think that in them you have eternal life; and it is these that bear witness of Me;
ACT 17:2= And according to Paul's custom, he went to them, and for three Sabbaths reasoned with them
from the Scriptures,
JOH 20:30= Many other signs therefore Jesus also performed in the presence of the disciples, which are not written in this book; but these
have been written that you may believe that Jesus is the Christ, the Son of God; and that believing you may have life in His name.
ROM 1:16= For I am not ashamed of the gospel, for it is the power of God for salvation to everyone who believes, to the Jew first and also to the Greek. For in it the righteousness of God is revealed from faith to faith;
as it is written, "But the righteous man shall live by faith."
1JO 5:13= These things
I have written to you who believe in the name of the Son of God, in order that you may know that you have eternal life.