When the Israelites entered the Promised Land the Amalekites had “tripped them up.” That is, they attacked the Israelites at their weak spot, or at their hindermost part or “tail,” which was comprised of those people who had lagged behind (Deut 25:17).
The Hebrew word for the hindermost part of the body is עָקֵב, which is used in the Hebrew Bible to refer to the rear echelon of an army (Genesis 49:19 and Joshua 8:13). That is, the rear echelon of an army is their hindermost part. The Amalekites attacked Israel at their hindermost part or “tail.”
The exact same Hebrew word is also found in Genesis 3:15, where the serpent bites the "hindermost part" of the promised seed of the woman -- that is, the serpent is to attack his heel, since the heel is physiologically the hindermost part of the human body. The seed of the serpent is therefore the enemy of God. It is the intent of the seed of the serpent “to trip up” the seed of God.
“Amalek” therefore is the enemy of the seed of God (Israel), who “trips up” at the most vulnerable time and opportunity. In the context of the Torah, the Amalekites in Canaan were not the seed of the Amorites, the Hittites, the Perizzites, the Canaanites, the Hivites or the Jebusites, but of Esau (Genesis 36:12). When Esau was born, his twin brother tried “to trip him up” at birth, and therefore the twin brother was named “Jacob.”
Genesis 25:24-26 (NASB)
24 When her days to be delivered were fulfilled, behold, there were twins in her womb. 25 Now the first came forth red, all over like a hairy garment; and they named him Esau. 26 Afterward his brother came forth with his hand holding on to Esau’s heel, so his name was called Jacob; and Isaac was sixty years old when she gave birth to them. (Emphasis added)
Please note that “Jacob” (יַעֲקֹב) and “heel” (עָקֵב) are related etymologically in Hebrew. Later in his life, Jacob will deceive his father Isaac in order to inherit the blessing of the firstborn -- that is, Jacob had recognized the promises made to Abraham, and so he STROVE to seize those promises made to Abraham and Isaac. In his deception scheme, Jacob “tripped up” his brother Esau to this end. First he seized legal right to the birthright from Esau in exchange for a mess of pottage, when Esau was most vulnerable because of hunger. Secondly, he later schemed with his mother (Rebecca) to seize the blessing from his father, Isaac, through deception by pretending to be Esau. Because Jacob was persistent to seize the Abrahamic promises from men like his brother Esau and his father Isaac, and because Jacob was persistent to seize some blessing of promise from the Angel of the LORD in Genesis 32:28, the Angel of the LORD changed his name from one who “trips up” to one who “persists” or “strives with God” (Israel).
In other words, the Angel of the LORD sanctified the identity of the man who once had manipulated people as his modus operandi of life and living, to one who now was the seeker of God and his promises. His name was no longer to be “Jacob” (one who trips up others through manipulation), but was now to be “Israel” (one who strives with God [for the Promises made to Abraham and Isaac]).
So in the Biblical narrative, the promised seed of the woman now becomes the promised seed of Abraham, which passes from Abraham to Isaac, and now Isaac to Jacob (Israel), whose sworn enemy will remain Amalek. Throughout the Hebrew Bible, Amalek later appears “to trip up” Israel when Israel had failed “to strive after God.” For example, Haman the Agagite (Book of Esther) was an Amalekite.