TT points to R. Zecharyah in the name of R. Yishmael: the priesthood was to have gone forth from Shem; because he put Avraham’s blessing before the blessing of the Place, it was taken from him and given to Avraham.
English of Core Text: R. Zecharyah said in the name of R. Yishmael: the Holy One sought to bring forth the priesthood from Shem; once he put the blessing of Avraham before the blessing of the Place, He took it from him… Avraham said to him: Does one put the blessing of the servant before the blessing of his Master? Immediately it was given to Avraham.
On the daf / in context: The order of Malki-Tzedek’s two blessings is treated as a decisive error that transfers the kehunah line.
Type of Learning
Custom
What Is Learned
Priority in blessing reflects priority in relationship; mis-ordering cost Shem the priesthood.