There are two major sources I rely upon:
First, scripture - God was there, I was not, so I value those "first person" reports.
Second, observations of creation itself.
Being a fallible human, I can only "approach" truth without being certain as to my conclusions. I also rely upon interacting with other humans.
As beings made in God's image, I believe we have a shot at figuring things out through study, observation, experimentation, and the application of reason. However, I don't expect to know "the final answers" until I am able to question God directly.
Thanks for your thoughtful comments. ;)
Have you looked into the targums? These Hebrew writings help one understand how the Jews of Jesus' time approached Scripture. Think of them as sermon notes from the Pharisees and Priests of the time.
Thank you for the mention. I do interact with people still in the Jewish faith, and try to learn from them. I appreciate your recommendation. :D