Sometimes someone runs into his misfortune, and when he finally realizes it, he still says reproachfully, "Couldn't you have warned me?" It is similar in today's Gospel (Lk 16:19-31): poor Lazarus goes to heaven, the wicked rich man to hell. There he sits and repents of his life - too late. Now he wants to warn at least his family, so that they change in time. And Jesus says (or rather he lets the wise Abraham say in the story):
If they do not listen to Moses and the prophets,
they will not be persuaded,
when one rises from the dead.
Lk 16, 31
Clear case: we actually know exactly how we should live. We do not always need further revelations and signs. Everything has been said long ago. Only we have to do it.