Or HaChaim on Genesis 48:15/אור החיים על בראשית מ״ח:ט״ו

1 ויברך את יוסף, He blessed Joseph. We do not find a blessing addressed to Joseph here. Nachmanides says that by blessing Joseph's sons Jacob actually blessed Joseph. This does not really appeal to me as it does not explain why Jacob did not say some words which would apply to Joseph individually. I believe that the very word ויברך was Jacob's way of telling Joseph that he would remain blessed henceforth.

2The wording may also be explained in terms of Bereshit Rabbah 39,11 that Abraham received the keys to blessings. Isaac received those keys after Abraham had died and he handed them to Jacob before he sent the latter to get himself a wife. At this point Jacob bequeathed these keys to his son Joseph. This is the meaning of the words ויברך את יוסף.

3ויאמר האלוקים אשר התהלכו אבותי לפניו, He said: "the G'd before Whom my forefathers walked, etc." Jacob recited the virtues of his forefathers before commencing his blessing much as we do when we commence the central prayer the עמידה, where we first introduce ourselves to G'd as descendants of worthy people. Jacob did not spell out the specific merits of his fathers, but when he spoke about himself he added that his own conduct had been similar to that of the sheep which walks in front of the shepherd who looks after it. Only after this introduction did Jacob commence his blessing with the words: המלאך הגואל.