Magic

Magic can be seen in many forms throughout the Light novels, its split into 3 main categories, God-based magic, Elemental-based magic and Otherworldly Magic, with a 4th category for magic we're not sure of.

God-based Magic
While there are 3 classes that utilise this magic we've only see 2 gods that have magic of their own, Skullheil and Lumiaris, with Priests and Paladins utilizing the magic of Lumiaris and Dread Knights utilising the magic of Skullheil. While Hunters do follow a god (Eldritch) we have not seen any magic surrounding them.

3 classes that we have seen so far use this type of magic are Paladins, Priests and Dread Knights. The world that you are in seems to greatly affect the potency of God-based magic, In the Dusk Realm such magic does not work at all, most likely meaning the gods have no influence over worlds they've never been to. Darunggar hampers the functionality of God-based magic to 1/3rd of its original power as seen in Grimgar.

Elemental-based Magic
Only one guild so far has used this magic, the Mage Guild.

Otherwordly Magic
Magic exclusive to otherworlds, Parano being the main example.

Unknown Magic
Currently Shaman magic, necromancy and Relics are unknown in origin and have very little information surrounding them, we do know that Shamans have the ability to heal much like priests and paladins (as seen when Jessie smith brings Haruhiro to his shaman).

Necromancy seems to be unusual for magic as it requires the use of relics and the injection of fluid into the Golem. Its very possible that the entire school of necromancy is solely based on relics.