Tosfos concludes that bracha rishona is an asmachta (ie d'rabanon). However, why wouldn't we say its doraisa? The gemara concludes that bircas hanehenin are derived from a sevara and we see elsewhere that the gemara considers a sevara as even a stronger reason than a drasha
Gary Schreiber, chicago IL
An excellent question, one, to be honest, that has bothered me for ages.
Incidentally, Tosfos merely concludes that the Pasuk first quoted is an Asmachta, not The B'rachah Rishonah, which could be d'Oraysa, if not for the Gemara in 'Mi she'Meiso', which considers it de'Rabbanan.
The Rashba, commenting on the S'vara 'Asur le'Adam ... ', connects it with the Pasuk cited shortly "la'Hashem ha'Aretz u'Melo'ah". If the land belongs to Hash-m, he explains, how can one possibly benefit from it without permission? Were it not for this Pasuk, we would presumably have thought that, having created the world for our benefit, it is now ours to do with as we please, and no B'rachah is necessary (interestingly enough, Chazal do say, with regard to Torah, that Hash-m gave it to us in its entirety). Now the Pasuk under discussion is in Tehilim, and not in the Torah. Consequently, even though the B'rachah Rishonah is a S'vara, it can only be mi'de'Rabbanan, since the S'vara's source is a Pasuk in Nach.
R. Eliezer Chrysler