Genesis 30:9 - Joseph Benson’s Commentary on the Old and New Testaments

Rachel had absurdly and preposterously put her maid into her husband's bed; and now Leah, because she missed one year in bearing children, doth the same, to be even with her. See the power of rivalship, and admire the wisdom of the divine appointment, which joins together one man and one woman only. Two sons Zilpah bare to Jacob, whom Leah looked upon herself as entitled to, in token of which, she called one Gad, promising herself a little troop of children. The other she called Asher, happy, thinking herself happy in him, and promising herself that her neighbours would think so too.