Langacker views language as a symbolic representation, and in his view grammar is “imagic” because it structures the symbolization of the conceptual content of the speaker/writer. Thus, the grammar we use to convey a concept reflects our particular construal of that concept, or it may reflect how we want our reader/listener to construe that concept. A ready example is active v. passive constructions: Fritz kissed Rita/Rita was kissed by Fritz. Although we can recognize that in both sentences Rita was kissed, the meanings of the two sentences are slightly different and represent slightly different “images” of the act.

Maybe you should check out Langacker's (2002) book "Grammar and Conceptualization". In chapter 7 "Viewing in cognition and grammar" he outlines his idea that conceptualization works analogously to visual perception. The result is that conceptualization is just as "imagic" as visual perception is. To get grammar in, add Langacker's assumption that every grammatical structure has semantic import. That means differences in grammatical structures are associated with differences in conceptualization/construal. And because the latter have an imagic basis, grammar has, too.