Let all mortal flesh keep silence (Ancient Greek: Σιγησάτω πᾶσα σάρξ βροτεία), also known as Let all mortal flesh keep silent, is an ancient chant of Eucharistic devotion based on words from Habakkuk 2:20, "Let all the earth keep silence before him" (Hebrew: הַ֥ס מִפָּנָ֖יו כָּל־הָאָֽרֶץ has mippanaw kol ha-arets, Septuagint: ὁ δὲ κύριος ἐν ναῷ ἁγίῳ αὐτοῦ εὐλαβείσθω ἀπὸ προσώπου αὐτοῦ πᾶσα ἡ γῆ) and Zechariah 2:13, "Be silent, all flesh, before the LORD; for he has roused himself from his holy dwelling" (Hebrew: הַ֥ס כָּל־בָּשָׂ֖ר מִפְּנֵ֣י יְהוָ֑ה כִּ֥י נֵעֹ֖ור מִמְּעֹ֥ון קָדְשֹֽׁו׃ ס. Septuagint: εὐλαβείσθω πᾶσα σὰρξ ἀπὸ προσώπου κυρίου διότι ἐξεγήγερται ἐκ νεφελῶν ἁγίων αὐτοῦ).

In modern times, the Ralph Vaughan Williams arrangement of a translation from the Greek by Gerard Moultrie to the tune of "Picardy", a French medieval folk melody, popularized the hymn among other Christian congregations.

Rex enim regnantium, Christus Deus noster, prodit ut mactetur deturque in escam fidelibus, praecedunt autem hunc chori angelorum cum omni principatu et potestate, cherubim multis oculis et seraphim sex alis praedita, facies velantia et vociferantia hymnum, alleluia.

Let all mortal flesh keep silence, And with fear and trembling stand; Ponder nothing earthly-minded, For with blessing in His hand, Christ our God to earth descendeth, Our full homage to demand.

[4] According to Philip Moore: The music captures the words perfectly with the sombre opening in octaves, followed by high voices lifting the mind 'above all earthly thought'.

There is a massive build-up through the 'choirs of angels' to the Alleluias, and the music eventually subsides with a magical harmonized version of the opening, complete with a cadence of unusual power.