One commentator points out that the black raven, a scavenger, is an unclean bird (Lev 11:15); it wandered here and there (as Satan did; so he said in response to God, after returning “From going to and fro in the earth”; see Job 1:7). Meanwhile, the white dove is gentle, quiet, and here, returned with evidence of renewed life, of an olive tree that might was good for food and oil. It is perhaps not surprising that the dove became a symbol of the Holy Spirit, particularly after the Holy Spirit descended bodily to Jesus (e.g., Matt 3:16). Interesting, these two birds are sent forth at the end of a 40-day period, just as the twelve spies were sent (Num 13:2) to learn about the Promised Land (but at the beginning of a 40-year period). In both cases, one portion was unfaithful and worthless (ten of the Israelites, and the raven), and another portion was faithful and helpful (Joshua, Caleb, and the dove).