So we are working on the idea that many times an element needs commas around it in the sentence but that this does not necessarily mean that element is "nonessential" or "isn't necessary to the meaning of the sentence."
A parenthetical is an element that can be dropped into any sentence we say. We can say "well" somewhere in every sentence we say. We can say "in my opinion" in every sentence we say. We surround these with commas. However, we are not surrounding them because they are "nonessential."
If my sentence is "He is guilty, in my opinion, of this most heinous crime," it changes the basic meaning if we take out "in my opinion." The sentence gives a different meaning without "in my opinion," but we still surround "in my opinion" with commas.
We don't surround elements with commas in sentences solely because they are "not necessary to the meaning of the sentence." We surround some things with commas that really do make a difference to the meaning of the sentence.
More to come...
Happy punctuating!
Margie