Invocation is the imagination of a deity and the subsequent identification with this imagined image of the deity. This procedure is one of the basics of magic, because through such an identification one's own possibilities of perception and action become many times greater.
This technique goes back to the late Paleolithic Age, when hunters identified themselves with a panther in order to obtain the strength and speed of a panther during their hunt. Later, the grain god was invoked in the Neolithic period, and then the One God was invoked in kingship.
The effectiveness of the technique of invocation, of course, like all magical phenomena, cannot be proven by words, but at least described in such a way that you may try this technique yourself.
As with almost all things, patience and practice are beneficial, but there are also some methods, such as dream travel, that make the whole thing much easier and more effective.