John Calvin Commentary Genesis 32:6

"And the messengers returned to Jacob, saying, We came to thy brother Esau, and moreover he cometh to meet thee, and four hundred men with him." — Genesis 32:6 (ASV)

And the messengers returned. Esau advances to meet his brother with a feeling of benevolence: but Jacob, reflecting on his cruel ferocity, inflated spirits, and savage threats, expects no humanity from him. And the Lord willed that the mind of his servant should be oppressed by this anxiety for a time, although without any real cause, in order to further excite the fervor of his prayer.

For we know what coldness, on this point, security engenders. Therefore, so that our faith, not being stirred up by any stimulants, does not become torpid, God often allows us to fear things that are not terrible in themselves. For although he anticipates our wishes and opposes our evils, he still conceals his remedies until he has exercised our faith.

Meanwhile, it should be noted that the sons of God are never endowed with a constancy so steadfast that the infirmity of the flesh does not betray itself in them. For those who imagine that faith is exempt from all fear have had no experience of the true nature of faith.

For God does not promise that he will be present with us to remove the sense of our dangers, but so that fear may not prevail and overwhelm us in despair. Moreover, our faith is never so firm at every point as to repel wicked doubts and sinful fears, as completely as might be wished.