Ignoring the Catholic bash (my question was to sola believers...what I hear you saying is that if two such believers come to different conclusions (which they do on many important and vital matters) then one of them is simply not listening to the Holy Spirit. Please confirm that is what you are saying.
There is only one “vital matter”.
“believe on the Lord Jesus and you will be saved – and your house”.
What other "vital matter" could you possibly be talking about?