imperial edict
詔 centers on an official proclamation from a ruler: an imperial edict, a formal command issued by the emperor.
詔 combines 言 (speech, words) with 召, which likely contributes the sound and carries a sense of summoning or calling forth, fitting the idea of an imperial proclamation.
Words (言) that summon (召) the people: an imperial edict is a formal call to action or announcement from the throne.
For ショウ, imagine a show of imperial power: the emperor's edict is announced with a grand show -> ショウ.