860. 'The number of whom is as the sand of the sea' signifies the multitude of such. The multitude of them is compared to 'the sand of the sea' because by 'the sea' is signified the external of the Church (n. 402-404, 470) and by 'the sand' that which serves no other use in the sea than to make the bottom of it. Because the number of them is so immense it is therefore called:-
The valley of their burial, the Multitude of God, and the name of the city where they are, the Multitude Ezek. xxxix 15 [, 16].