Luke 16:27-31
27 “He answered, ‘Then I beg you, father, send Lazarus to my family, 28 for I have five brothers. Let him warn them, so that they will not also come to this place of torment.’
29 “Abraham replied, ‘They have Moses and the Prophets; let them listen to them.’
30 “‘No, father Abraham,’ he said, ‘but if someone from the dead goes to them, they will repent.’
31 “He said to him, ‘If they do not listen to Moses and the Prophets, they will not be convinced even if someone rises from the dead.’”
“...listen to them...”
Listening is not writing. Nowhere does the bible say that scripture alone is to be used to shape doctrine. Nowhere.
The Jews followed an oral tradition and the early Christians did as well. The gospels started out as oral tradition.
The bible does not tell us that it alone is sufficient for salvation; in fact it tells us the OPPOSITE:
2 Tim 2:2 and 2 Thess 2:15
Also: John 21:25