Sforno on Genesis 21:22/ספורנו על בראשית כ״א:כ״ב

1אלוקים עמך, seeing that G’d clearly is on your side I am afraid of you. I am not afraid of your personal strength, but of that of your G’d. This is why I ask you to swear to me. [so that you cannot appeal to G’d’s assistance in any grievance you would have against me. Ed.]