You are thinking of the written language as the fundamental thing. Actually spoken language is fundamental, and writing is an imperfect representation of it.
The verb "lead" and the noun "lead" (i.e., the metal) are two different words, pronounced differently. The fact that they are spelled the same is just an example of how the English writing system doesn't encode the English language perfectly accurately.
The verb "lead" and the noun "lead" (i.e., the metal) are two different words, pronounced differently. The fact that they are spelled the same is just an example of how the English writing system doesn't encode the English language perfectly accurately.