The Line Editor
This is your final defense, the last step, the difference between being a writer with a good idea and a professional author.
The line editor generally isn’t there to discuss story arc or make sure you understand how to use a dialogue tag. Instead, they are there to make sure you are putting out the best quality product possible.
Line editors will go over each sentence to make sure it is ready for publication. They check for grammar, punctuation, spelling, consistency and word usage (Is he your Principle or your PrinciPAL?) and can often assist with rewriting/rewording sections that need help.
As you can see there are a lot of steps, and they are all important. In the end, the best thing you can do is find a group of people you trust with your work and get them on your team. Each step in the process will only make your manuscript better, and a professional edit is never wasted money.