April 21

Garden of Ridvan in Baghdad
…the world-wide celebrations of the “Most Great Festival,” the “King of Festivals,” the “Festival of God” Himself—the Festival associated with the accession of Him Who is the Lord of the Kingdom to the throne of everlasting glory, and with the formal assumption by Him of His prophetic office… 
(Shoghi Effendi from a letter dated June 15, 1946; ‘Messages to America’)