Malchi-Tzedek is a gentile priest who worships God.  I initially read this as just saying God is not exclusive (it says somewhere in Nevi'im that God also has covenants with other peoples), but today I read in *Tz'enah Ur'enah* that the priesthood was taken away from him and given to Avram because of the incident in torah (because he blessed Avram before praising God).  This seems to suggest that, had people acted differently, Avraham might not have had the role he ended up having.  How are we to understand Malchi-Tzedek?