Griffith survives the attempt because his Beherit, hanging around his neck, blocked the poisoned needle hidden in the cup or acted as a shield (depending on the interpretation of the "luck" it provides).
Griffith and his primary lieutenants (Guts, Casca, Rickert, Judeau, and Pippin) are honored by the King. This cements their transition from "mercenaries" to "nobles." Berserk Episode 10
The primary conflict is not with swords, but with status. The Midland "old guard" cannot stand a commoner rising so high. Griffith survives the attempt because his Beherit, hanging
The episode features beautiful, static backgrounds of the Midland palace, emphasizing the grandeur and "coldness" of the nobility. hanging around his neck