From A Lamp For My Feet by Elisabeth Elliot:

How can this person who so annoys or offends me be God’s messenger? Is God so unkind as to send that sort across my path? Insofar as his treatment of me requires more kindness than I can find in my own heart, demands love of a quality I do not possess, asks of me patience which only the Spirit of God can produce in me, he is God’s messenger. God sends him in order that he may send me running to God for help.