Genesis 32:6

6.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 the more to excite the fervor of his prayer. For we know what coldness, on this point, security engenders. Therefore, lest our faith, being stirred up by no stimulants, should become torpid, God often suffers us to fear things which are not terrible in themselves. For although he anticipates our wishes, and opposes our evils, he yet conceals his remedies until he has exercised our faith. Meanwhile it is to be noted, that the sons of God are never endued with a constancy so steadfast, that the infirmity of the flesh does not betray itself in them. For they who fancy 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 for the purpose of removing the sense of our dangers, but in order 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, in the way that might be wished.