The Pulpit Commentary on Genesis 16:9

And the angel of the Lord said unto her—as Paul afterwards practically said to Onesimus, the runaway slave of Philemon (vide Philippians 12)—return to thy mistress, and submit thyself—the verb here employed is the same as that, which the historian uses to describe Sarah's conduct towards her (Philemon 1:6); its meaning obviously is that she should meekly resign herself to the ungracious and oppressive treatment of her mistress—under her hands.