Personally I think logic -reasoning - common sense Also help understanding Bible teachings --
All scriptures on a teaching must be in agreement If not then checking other Bible translations may be Necessary -
Parables are never to be taken literally
Most of the time if symbolic language is used In a scripture - another scripture will give the Meaning For example - revelation 21 says there will be no more Sea in the cleansed new earth Isaiah 57 says the wicked are like the sea so What revelation meant is there would be no more Wicked -