Guardian Lore

With the turmoil in Elona and the spread of the Order of Whispers into other lands, more Paragon teaching showed elsewhere in Tyria. These teachings melded with other traditions, and over time, the Guardians and their abilities can be found throughout the world and among all the races. They are not tied to a particular race, philosophy, or group of gods but rather to a larger concept of proactive defense, of taking the fight to a foe and protecting those you fight alongside while appealing equally to humanity's defensive nature and the Charr's desire to rule the battlefield.

I think the Guardian is much more of a pragmatic and tactical user of a magic as opposed to an Elementalist, who is a pure student of magic. The Elementalist casts discrete spells, and you have the feeling that there is a heritage and body of knowledge behind those spells. Guardians seem to use magical energy in the heat of combat, from the front line. That sense of immediacy sets the Guardian apart from more traditional spell-casters and allows for a heavily armored magical character.