Magic functions via connections, and sympathy. In short, like effects like. Elementalists form miniature elemental replicas of large scale things they wish to affect, then manipulate the model to effect the original. Taking material from the target increases the strength of the connection and thus magic, for example, a magical doll of a rival with some of his plucked hair placed in it, so you could torture him using the doll.
Factors effecting connections are distance, similarity, familiarity with the target, whether the target can currently be sensed, knowledge of the target's secret truename, and more probably.
"How does one create a replica of an abstract concept? Sense it? Be familiar with it? Be close to it?"
That would depend on the concept in question. I believe the proposed system can adequately handle any of the somewhat more abstract concepts present in the default magic system of the bubble, and can explain more on this if it is required, but admit I did not really consider usage of abstract concepts beyond that, as this seemed overly powerful for what is intended to be a merely more defined general magic system.
However, god-tokens could probably give a bearer somewhat of a connection to the sphere of the god whose token it is. Or they could discover the true name of a concept, if such exists.
A mage could spy on a friend they are very familiar with who is ten miles away with the crystal figurine made to look like him, celestial mages draw power for spells from the stars through the connection of the stars with their past lives on the planet, divine mages use the principle of sympathy to imitate the miracles of the gods, the spell being fake worshipped as a fake god until it gains enough power.
"How does someone "fake" worship? What is to stop them convincing any less intelligent but still able to worship mortals that the "fake god" of their magic is actually entirely genuine, allowing them stronger magic while weakening actual gods by taking their income?
What does sympathy have to do with worship?"
The sympathetic connection, that is to say, the magical link that somewhat powers divine magic, is between fake worship, and the true worship that empowers gods.
As such, the diminishing of true worship would weaken divine magic, since it relies on the connection to true worship to function.
As to how one "fake" worships, this would be a case of going through motions, without substance. Where to your true god you might sacrifice a bull in a sacrificial pyre, for fake worship you burn a paper effigy. The similarities of sacrifice then power the magic. Praying to your god or creating clay figurines in poses of prayer, and so on.
The gods may hand down tokens to favoured mortals, granting them a connection to that god which can then be used to perform powerful magic, with the danger of the connection potentially being used against the god.
"You create a basic agent, and then give it a token to give it the power of a god. You now have something that will do everything you want it to, and no way for it to turn against you. You could then secretly task it with destroying things of value to the other gods, and once it is discovered destroy it yourself, leaving any trace of your influence easily explained away as residue from the destructive forces involved in its demise!"
The tokens do not make the bearers as powerful as a god. It merely gives them somewhat more powerful magic, perhaps on the level of elementalism. The token could be stolen from the hypothetical basic agent, and your enemy could then use the connection against you.