Use of comma in appositive

[Jupiter]

Hi teachers,

What is the difference between?

My brother, James, is ateacher.
My brother, James is a teacher.
My brother James a teacher.

Thanks in advance

Jupiter

[Jamie (K)]

My brother, James, is a teacher.
This means that you have only one brother, and you are telling us his name just as extra information. It means, "My brother is a teacher, and by the way, his name is James."

My brother, James is a teacher.
You are talking to your brother. You are saying, "Hey, brother! That man named James is a teacher." When you start out with "my brother" like this, we understand that you mean, "I am your brother, and I would not lie to you."

My brother James a teacher.
This means you have more than one brother, and the one you are talking about is named James. You need to say the name so that people know which brother you are talking about. It means, "One of my brothers -- the one named James -- is a teacher."