What's the purpose of differentiating the singular and plural forms of verbs? [closed]

It's not that I can't memorize them, but I have always been wondering how it has become the way it is - what's the purpose of differenting them?

Why not just always use the singular form?

I am a native Chinese, and in Chinese verbs don't differentiate singular/plural forms and even tenses.

I understand tenses can be useful, as they indicate the time of the action. But since the subjects can already indicate if the number is one or more, why not just use one certain form under all circumstances?

Languages evolve, they aren't designed.

English used to distinguish between 1st person singular, 2nd person singular, 3rd person singular, and plural subjects. And we also had cases, which meant we could rearrange the order of words without changing the meaning (e.g., man bites dog vs. dog bites man). In linguistic terms, English was a synthetic language like Latin and Russian.

When these distinctions were lost because people started dropping word endings, the language started using word order to eliminate any resulting ambiguity. The plural form of the verb is a residue of this earlier system. Its not clear to me that it is that useful in the current language—English would probably be nearly as easily understood without it—but we are certainly not going to drop it any time in the near future.