John Calvin on Genesis 18:5

5. For therefore are ye come to your servant He does not mean that they had come designedly, or for the express purpose of seeking to be entertained, as his guests; but he intimates that their coming had occurred opportunely, as if he would say, ‘You have not slipped into this place by chance; but have been led hither by the design and the direction of God.’ He, therefore, refers it to the providence of God, that they had come, so conveniently, to a place where they might refresh themselves a little while, till the heat of the sun should abate. Moreover, as it is certain that Abraham spoke thus in sincerity of mind; let us after his examples conclude that, whenever our brethren, who need our help, meet us, they are sent unto us by God.