Aesculapius, a famously talented doctor from Classical mythology, agrees to help Night bring back Sansjoy from death (a big no-no). In fact, Aesculapius really should know better, since bringing people back from the dead is what got him stuck in Night's realm in the first place.
The fact that Aesculapius accomplishes his medical miracles in a dark, secret cave associates his power with the secrecy and immorality of Night. In a Christian context, bringing someone back from the dead is a no-no for two importance reasons: 1) that kind of power should only be left to God and 2) the act mistakenly places importance in this mortal life when, if you believe in the Christian God, you should also believe in a Christian afterlife that is actually way better than this life. So Aesculapius is both overly proud but also foolish, since he values the wrong things.