“the angel.” This is agency. God blesses them, but does so through the angel. This is one of the places where a plural subject takes a singular verb (cp. Exod. 4:29, “Moses and Aaron went (the went is singular). Judges 5:1, “saying” is singular. 1 Kings 1:34, “anointed” is singular. 1 Kings 22:29, “went up” is singular; 2 Kings 10:23, “went” is singular but Jehu and Jehonadab went). It sometimes happens that a plural subject takes a singular verb. Gesenius says, “As in other languages, so also in Hebrew, the predicate, in general, conforms with the subject in gender in number...there are, however, exceptions to this fundamental rule.”a
“bless the lads.” The verb is singular. This has caused some theologians to say that God is a Trinity because here God and the angel are spoken of with a singular verb, “bless.” But there is much wrong with that logic. For one thing, it occurs a number of times in the Bible that a plural subject is paired with a singular verb (cp. Exod. 4:29 (“went”); Exod. 8:8; 10:3; Josh. 8:3; etc.). Also, in this case, the angel may have been representing God in this context, as angels often do; there is no “and” before “the angel,” so the angel could be representing God, and this would be a case of divine agency. That would make this verse about the representative of God, just like the angel who wrestled with Jacob and changed his name to Israel.