When Yaakov blesses Yosef’s children, he asks of God that “the angel that redeems me from all evil bless the lads” (48:16). Why does he ask God for the angel to bless them? Can God not bless the children himself? The Radak suggests that when God wants to do good, He does it through His angels. Therefore, Yaakov asks God to send an angel of good to bless the children. The problem with this answer, however, is that if God does all his good through the angels, we should always Daven for Hashem to send angels when we want good things to happen. Since it is not our practice to do so, we are motivated to find an alternative explanation as to why Yaakov asked for an angel.
The Seforno believes that Yaakov is requesting that if the children are not worthy themselves to be blessed by God, they should at least be blessed by an angel. Another approach is that of Rav Sa’adia Gaon and the Chizkuni, who assert that Yaakov is not actually asking for the angel to do anything; rather, he is describing God with an appositive phrase. Thus, the verse should be translated as, “God, Who sent an angel to redeem me from all evil, should bless the lads.” The question then becomes: of all things to praise God for, why specifically does Yaakov cite His having sent angels? Rashi answers this question by pointing out that Yaakov had a history with angels. For example, it was an angel who told Yaakov to go to Israel when he was still living in Lavan’s house. Similarly, Yaakov dreamed of angels on his way to Lavan’s house, and he encountered angels on the return journey at Machanayim. Since Yaakov was used to dealing with angels, it came naturally to him to speak in terms of angels.