God says in the bible salvation is only through Jesus and God does not lie
The reason God won't go beyond his word the bible on salvationor any other issue, is because God is not a liar, so does not lie.
If God said salvation is only through repenting and believing in Jesus in the bible, and then went beyond the bible and allowed people to be saved some other way, then that would make God a liar. And we know God is no liar.
God gave his written word to speak his truth and tell us how he operates. So people can't say, "God told me", when he didn't. It is a check on claims.
Salvation through Jesus verses:
Acts 4:12
"Nor is there salvation in any other, for there is no other name under heaven given among men by which we must be saved"
John 14:6
"Jesus said to him, 'I am the way, and the truth, and the life. No one comes to the Father except through me'"
John 3:16–18
"For God so loved the world, that he gave his only Son, that whoever believes in him should not perish but have eternal life"
Romans 6:23
"For the wages of sin is death, but the gift of God is eternal life in Christ Jesus our Lord"
John 5:24
"I tell you the truth, whoever hears my word and believes him who sent me has eternal life and will not be condemned; he has crossed over from death to life"
Bible is God’s word:
2 Timothy 3:16:
"Everything in the Scriptures is God's Word. All of it is useful for teaching and helping people and for correcting them and showing them how to live"
God does not lie verses:
Titus 1:2
"In hope of eternal life, which God, that cannot lie, promised before the world began".
Hebrews 6:18
"That by two immutable things, in which it was impossible for God to lie, we might have a strong consolation, who have fled for refuge to lay hold upon the hope set before us".
Numbers 23:19
"God is not man, one given to lies, and not a son of man changing his mind".