What are symbols? Why

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https://victorianweb.org/philosophy/langer1.html

As far as thought is concerned, and at all-levels of thought, it [mental life] is a symbolic process. It is mental not because the symbols are immaterial, for they are often material, perhaps always material, but because they are symbols. . . . The essential act of thought is symbolization. — A. D. Ritchie, The Natural History of the Mind

Symbolization is the essential act of mind

Not higher sensitivity, not longer memory or even quicker association sets man so far above other animals that he can regard them as denizens of a lower world: no, it is the power of using symbols—the power of speech—that makes him lord of the earth. So our interest in the mind has shifted more and more from the acquisition of experience, the domain of sense, to the uses of sense-data, the realm of conception and expression. The importance of symbol-using, once admitted, soon becomes paramount in the study of intelligence. . . . Symbolism is the recognized key to that mental life which is characteristically human and above the level of sheer animality. Symbol and meaning make man’s world, far more than sensation; Miss Helen Keller, bereft of sight and hearing, or even a person like the late Laura Bridgman, with the single sense of touch, is capable of living in a wider and richer World than a dog or an ape with all his senses alert. [33, 35]