Jacob said,
The God before whom my fathers Abraham and Isaac walked,
the God shepherded me all my life long to this day,
the angel who has redeemed me from all evil
bless (singular) Ephraim and Manasseh.
A triple reference to God, in which the Angel who is placed on an equality with God. He cannot possibly be a created angel. He must be the “Angel of God” i.e. God manifested in the form of the Angel of Jehovah, or the “Angel of His face” (Isa 63:9).
This passage contains a foreshadowing of the Trinity, though only God and the Angel are distinguished, not three persons of the divine nature.
The God before whom Abraham and Isaac walked, had proved Himself to Jacob to be “the God which fed” and “the Angel which redeemed”, i.e. according to the more fully developed revelation of the New Testament, Shepherd and Redeemer.
By the singular bless the triple mention of God is resolved into the unity of the divine nature.
(source: Keil & Delitzsch on Genesis 48:15-16)
[The Angel of his face] was the mediator of the preparatory work of God in both word and deed under the Old Testament, and the manifestation of that redeeming might and grace which realized in Israel the covenant promises given to Abraham (Gen 15).
(source: Keil & Delitzsch on Isaiah 63:9)
[The angel of the LORD] assures Hagar, as if speaking in the character of an ambassador from God, that "the Lord had heard her affliction" (Gen. 16.11). Yet he promises her, "I will multiply thy seed exceedingly," and she in return "called the Name of the Lord that spake unto her, Thou, God, seest me." He arrests Abraham’s arm when the patriarch is on the point of carrying out God’s bidding by offering Isaac as a sacrifice (Gen. 22.11, 12); yet he associates himself with Him from whom "Abraham had not withheld his son, his only son." He accepts for himself Abraham’s obedience as rendered to God, and he subsequently at a second appearance adds the promise, ""In thy seed shall all the nations of the earth be blessed ; because thou hast obeyed My voice." He appears to Jacob in a dream; he announces himself as "the God of Bethel, where thou anointedst the pillar, and where thou vowedst a vow unto Me" (Gen. 31.11,13). Thus he was "the Lord" who in Jacob’s vision at Bethel had stood above the ladder and said, "I am the Lord God of Abraham thy father, and the God of Isaac." He was, as it seems, the chief of that angel-host whom Jacob met at Mahanaim (Gen. 32. 1); with him Jacob wrestled for a blessing at Peniel; of him Jacob says, "I have seen God face to face, and my life is preserved." When blessing the sons of Joseph, the dying patriarch invokes not only "the God which fed me all my life long unto this day," but also "the Angel which redeemed me from all evil."
(source: http://www.gospelpedlar.com/articles/Christ/liddon4.html)
Andrew Groves 