This teaches patience. While others are actively concerned in some enterprise, there must be those who play a passive part, but without whom the enterprise may fail. Again, many people – firemen, for example – must remain idle at their posts until an emergency suddenly arises.
The proverb is the last line of Milton’s sonnet on his blindness, which he feared would prevent him from writing and thereby serving God. He consoled himself with this thought :
– God does not need
Either man’s work, or His own gifts: who best
Bear His mild yoke, they serve Him best: His state
Is kingly; thousands at His bidding speed
And post o’er land and ocean without rest: –
They also serve who only stand and wait.