We don't know either.

I suspect it's to make English speakers sound funnier when they try to speak other languages. They always mess the genders up and it's kind of hilarious.

To make their language more confusing and complicated...?

Well you see nouns are like people, in that they have genders. However when a langauges doesn't acknowledge that the nouns get very angry and threaten to destroy all communication. So in order to calm them down other languages acknowledge their genders and save communication.

Fun Fact: Old English had gendered nouns.

Also some genered nouns are interestingly weird for example vestido is Spanish for dress as in that article of clothing women wear. It is a masculine noun. Don't think about that too much.

To contain more morphemes (i.e., more meaning) in a word. Of course, noun class does better at that than grammatical gender.

What's most interesting: Gender affects a speaker's ideas of a noun. For instance, Spanish-speakers find bridges sturdier (and more "manly") than German-speakers.

Also, words can be reused with a different article. For instance, el papa vs. la papa in Spanish -- the former is the Pope, the latter a potato. This also led to the hilarious situation where, after the Pope visited a certain Spanish-speaking area, a vendor made the mistake of selling shirts with the text "I saw the potato."

~B~

To make it harder for those filthy English to poison our native tongue by trying to learn it.