From John Calvin’s commentary on Genesis 32:
[T]he Lord willed that the mind of his servant (Jacob) should be oppressed by this anxiety for a time, although without any real cause, in order the more to excite the fervour of his prayer….For although he anticipates our wishes, and opposes our evils, he yet conceals his remedies until he has exercised our faith.
We, also, are to learn from him, that we must fight during the whole course of our life; lest any one, promising himself rest, should willfully deceive himself. And this admonition is very needful for us; for we see how prone we are to sloth. Whence it arises, that we shall not only be thinking of a truce in perpetual war; but also of peace in the heat of the conflict, unless the Lord rouse us.