To understand this passage, you have understand the story of Jacob and Esau from the beginning (which begins at Genesis 25:19). They were twins, and rivals. Jacob’s very name means “usurper” or “supplanter,” because he was born grasping the heel of his brother who was born first. He then gained Esau’s birthright in exchange for a pot of stew, when Esau was hungry after a long hunt, and then usurped the blessing he would have received from their father Isaac by trickery, and with the help of his mother. So Jacob’s very name pointed to a flaw in his character. He left Canaan to go to his uncle Laban because his mother feared Esau would kill him. While in Haran, Jacob found himself on the receiving end of trickery, when his uncle tricked him into marrying Leah after seven years of laboring for the hand of Rachel. After laboring seven more years for Rachel, and then laboring more to gain cattle, Jacob finally left his uncle, and began the journey home.
On his way to Haran, Jacob had an encounter with God at Bethel, which was the beginning of his spiritual journey. This incident happened the night before Jacob would meet, after so many years, the brother he had wronged. All his family and all that he owned had crossed over the river, and he remained behind this night. He justly feared for his life and the lives of his family. And so during this night Jacob wrestled with an angel, which the Fathers tell us was the pre-incarnate Christ.
St. Ambrose writes:
“Therefore Jacob, who had purified his heart of all pretenses and was manifesting a peaceable disposition, first cast off all that was his, then remained behind alone and wrestled with God. For whoever forsakes worldly things comes nearer to the image and likeness of God. What is it to wrestle with God other than to enter upon the struggle for virtue, to contend with one who is stronger and to become a better imitator of God than the others are? Because Jacob’s faith and devotion were unconquerable, the Lord revealed his hidden mysteries to him by touching the side of his thigh. For it was by descent from him that the Lord Jesus was to be born of a virgin, and Jesus would be neither unlike nor unequal to God. The numbness in the side of Jacob’s thigh foreshadowed the cross of Christ, who would bring salvation to all people by spreading the forgiveness of sins throughout the whole world and would give resurrection to the departed by the numbness and torpidity of his own body. On this account the sun rightly rose on holy Jacob, for the saving cross of the Lord shone brightly on his lineage. And at the same time the Sun of justice rises on the person who recognizes God, because he is himself the everlasting Light” (Jacob and the Happy Life 7:30, quoted in Ancient Christian Commentary on Scripture: Old Testament, Vol. II, Mark Sheridan, ed. (Downers Grove, IL: Intervasity Press, 2002) p. 218f)).
St. Augustine writes:
“So what does it mean, Jacob’s wresting and refusing to let go? The Lord says in the Gospel, “The kingdom of heaven suffers violence, and those who act violently plunder it [Matthew 11:12].” This is what we were saying earlier on: struggle, wrestle, to hold on to Christ, to love your enemy. You hold Christ here and now if you have loved your enemy. And what does the Lord himself say, that is, the angel in the person of the Lord, when he had got the upper hand and was holding him fast? He has touched the hollow of his thigh, and it has withered, and so Jacob was limping. He says to Jacob, “Let me go, it is already morning.” He answered, “I will not let you go unless you bless me.: And he blessed Jacob. How? By changing his name: “You shall not be called Jacob but Israel; since you have got the upper hand with God, you shall also get the upper hand with men.” That is the blessing. Look, it is a single man; in one respect he is touched and withers and in another he is blessed. This one single person in one respect has withered up and limps; in another he is blessed to give him vigor” (Sermon 5:6, quoted in Ancient Christian Commentary on Scripture: Old Testament, Vol. II, Mark Sheridan, ed. (Downers Grove, IL: Intervasity Press, 2002) p. 220)).
It is important to note that the Angel asked Jacob to state his name, which was in a sense a confession of his sinful past of usurpation and deception. He is given a new name, and this incident is an image of the spiritual purification and perfection that Christ can work in the lives of those who like Jacob, struggle for virtue, and prevail.