HA is focused more on support and healing, but does offer minor offensive capabilities. Mages are focused more on utility and offense with minor defensive options. I haven't worked out any kind of battle system and for now, most of the class options and abilities will have more of an affect on dialog and story branching until if/when I add minimal combat. An example of this would be the mage character finds himself in a cave with two tunnels, one is lit with torches, the other is dark. If the mage character knows the light spell, there will be an option to travel down the dark path instead of the lit path. The game won't really be a full RPG with battle systems and experience points, etc.
It will be described in more detail in game during the coming days of the HA major, but users of the holy arts do rely on spiritual allies and form contracts with spirits in order to access and channel magical power. Whereas mages directly access and manipulate the magic within the world itself rather than channeling through another source.