As a writer, I string words together on a page like beads on a necklace.
Have you ever noticed how the string is the most important part of a beaded necklace? When it's in place all you see is a beautiful piece of iridescent jewelry.
Break it, and you're left with a pretty pile of colored rubble.
This metaphor explains why grammar is so important to your writing.
Think of the words on your website as beads, and grammar as the string that holds it all together. If your grammar is correct it will likely go unnoticed and unappreciated. Poor grammar, however, sticks out like shards of broken glass.
This is because grammar is the glue that holds language together. It dictates how words go together to give them meaning and value. If readers have to re-read your website because they don't understand what you're trying to say, you're going to lose business, plain and simple.
If you struggle with grammar then hire a professional to write content for you. A good writer will use word choice and sentence structure to hook the reader and interest them in what you have to say (and sell). Only then can you convert website visitors into customers.
In short, good grammar = money. So you've got to get it right.