Rachel is first named here, as also Ruth 4:11, because she was his chief, and, by right, his first and only designed wife. And therefore it is observable, that in the enumeration of Jacob's wives and children, Genesis 46:1-34, Leah is only mentioned by her name, Genesis 46:15, but Rachel is called Jacob's wife, Genesis 46:19, by way of eminency, and in a peculiar manner. In the field they might more freely discourse of their business, and without fear or interruption.
Related Commentaries of Genesis 31:4
Genesis 31:4
4 And Jacob sent and called Rachel and Leah to the field unto his flock,