A good editor is worth their weight in gold.
When you read a book or magazine article it will always have been written by one person, then edited and checked by someone else. There’s a reason at least two people are involved in the print publishing process.
When you write a blog post yourself it’s hard to read it properly and notice the typos and errors. We tend to scan anything we wrote ourselves and can easily miss errors that would jump straight out at someone reading it for the first time.
Also, when you try to edit your blog post, you’re too close to the material and may skip over certain info, assuming your readers already know it just because you do.