The Weave was shattered many years ago and most of the threads of the Weave, that existed as a net around the material plane, disappeared with The Great Exodus. The remaining threads, as it is metaphorically referred to, still lay as a thin veil of threads around and woven into the plane as before, but the threads are scarce, and fewer strains flow through people, which has altered the relationship between civilization and magic to rely pretty heavily on either otherworldly power or Glister.
While most people are without magic, there are some who can manipulate what is left of the Weave to some extend;
Sorcerers. They still need Glister to work their magic, but not as heavily as others.
Wizards have the intellect to know how to efficiently convert Glister into magic.
Artificers have a similar ability though they need objects to keep control over the essence once drawn.
Paladins and other half casters have learned to do the same thing but seeing as it is more through force of will and a natural instinct, this is not as powerful.
Clerics and Warlocks fall under the same category of another being using them as a door for their magic to the material plane.
Bards use their imagination, creativity, and non-magical tools as extensions of themselves to the extend of controlling the wave lengths of magic for their own use.
Natural magic comes from the raw magic found in the world around us, and Druids more so than Rangers, can pick up on and to an extend manipulate this with some help of the power that comes from the Feywild. Shadow monks have the same ability but gets its spark from the Shadowfell instead.
Barbarians, Monks, Rogues, and Fighters all have in common that their magical essence is less tangible and rather useless unless honed.