Discuss many things -- science, religion, philosophy, reincarnation,... all of humanity's thoughts and progress.
Teach the value of humility and restraint in holding onto any belief, no matter how much supposed proof there is. There remain many mysteries yet to be solved.
There is great wisdom in the older religions and even in some newer ones, but there are also so many messy and inaccurate interpretations of them.
Finding your way in this area is done largely by feel, but also some logic and an enormous helping of humility. Without humility, even scientists miss out on discoveries.
Teach others to ask probing questions rather than to spout dogma. Teach them to be ever searching for answers, rather than sitting back, thinking that all the answers are already known.