Now the ‘masters of voices and speech’, – in hymns and praises and thanksgiving of prayer – are knocking, and the ‘masters of voices’, who call to the blessed Holy One in the recital of the Shm’a: (Deut. 6:4) Hear O Israel... – twice: morning and evening.
Meanwhile, the ‘masters of feet’ are knocking at the entrance – the masters of the ‘standing’ (’amidah) of prayer – of whom it is stated: (Dan. 1:4)... and who have the strength to stand, in the chamber of the King...
The King... unspecified – this is the blessed Holy One,cSee Esther Rabbah 3:10... the chamber of the King – this is ADNY, of which it is stated: ADNY! Open my lips... (Ps. 51:17) ADNY (=65) amounts to the numeric-value of HeYKHaL (chamber, =65). And it is stated: (Hab. 2:20)... and Ha-Shem in His holy chamber, let the whole Earth be silent (HaS, =65) before Him.