John Calvin Commentary Joshua 2:12

"Now therefore, I pray you, swear unto me by Jehovah, since I have dealt kindly with you, that ye also will deal kindly with my father`s house, and give me a true token;" — Joshua 2:12 (ASV)

Now, therefore, I pray you, swear, etc. It is another manifestation of faith that she regards the sons of Abraham as already in sure possession of the land of Canaan, basing this on no other argument than her having heard that it was divinely promised to them. For she did not suppose that God was favoring lawless intruders who were forcing their way into the territories of others with unjust violence and unrestrained licentiousness. Instead, she concluded that they were coming into the land of Canaan because God had assigned them dominion over it.

It cannot be believed that when they sought passage from the Edomites and others, they said nothing about where they were going. Indeed, those nations were aware of the promise made to Abraham, the memory of which had been renewed by the rejection of Esau.

Moreover, in Rahab's language, we see that characteristic quality of faith described by the author of the Epistle to the Hebrews, when he calls it a vision, or sight of things not appearing (Hebrews 11:1). Rahab is living with her people in a fortified city, and yet she entrusts her life to her terrified guests, just as if they had already gained possession of the land and had full power to save or destroy as they pleased.

This voluntary surrender was, in fact, the same as embracing God's promise and casting herself on His protection. Furthermore, she demands an oath, because often, in the storming of cities, the heat and tumult of the struggle caused people to forget their duty. In the same way, she mentions the kindness she had shown them, so that gratitude might further motivate them to perform their promise.

For although the obligation of the oath should in itself have been effective, it would have been doubly base and inhumane not to show gratitude to a hostess to whom they owed their deliverance. Rahab shows the kindness of her nature in her anxiety for her parents and relatives. This is, indeed, natural; yet many are so devoted to themselves that children do not hesitate to ransom their own lives by the death of their parents, instead of exerting courage and zeal to save them.