With the intervening comments it may be hard to remember that the "wherefore" that begins verse 3 is directly tied to the consecration of the Jacob's afflictions to his gain. Lehi indicates that the Lord will consecrate them for his benefit, and then explains that benefit (introduced by the "wherefore"). On account of the afflictions (or more properly his reaction to his afflictions) Jacob will be blessed, and is granted safe dwelling with Nephi, and a life in the service of God (born out by Nephi's citations of Jacob's teachings, 2 Nephi chapters 6-11).
The next section of this sermon is subtle, because it both defines Jacob's character, and lays another cornerstone for the discussion to come. Lehi shifts the focus slightly by moving from Jacob's character specifically to the Savior and his mission. While this flows naturally from Jacob's character, and fits precisely with Lehi's blessing of Jacob, it nevertheless also moves from the specifics of Jacob's blessing to the sermon that Lehi wants to preach.