No matter how many rules you know for commas, every one of those uses for the comma fits into one of two categories:
1. You are using a comma to separate two elements. You are using the comma to push two elements apart so that they do not pile up on each other.
...on June 5, 2012...
...in El Paso, Texas...
...was very, very difficult...
OR
2. You are using a pair of commas around an element. When you put commas around an element, you are saying it can be removed from the sentence and that you will still have a grammatically complete sentence.
...saying, ma'am, that she was...
...with my oldest brother, John Walker, and his...
...was living, you know, with my...
When you surround something, you are NOT saying it is "nonessential" to the meaning of the sentence. That term is restricted to a very specific situation. You are NOT saying that you don't "need" the element. There are many elements that are surrounded with commas and many reasons for doing so. It is not about you "don't need it."
To say "I am going to put commas around it because it can be taken out" would lead to a whole slew of commas that would not be correct. To say "This sentence is a run-on; so I need commas around something" is simply not consistent with the way the language works. To say "This element is not essential to the meaning of the sentence" is a very broad brush to use for some rules that apply to a very few situations.
Sometimes the grammar just needs commas around an element.
Every single comma rule goes into one of these two categories.
You are separating elements, or you are surrounding elements.
More to come...
Happy punctuating!
Margie