E. Cobham Brewer 18101897. Dictionary of Phrase and Fable. 1898.
To walk softly. To be out of spirits. In Greece, mourners for the dead used to cut off their hair, go about muffled, and walk softly to express want of spirit and strength. When Elijah denounced the judgments of heaven against Ahab, that wicked king fasted, and lay in sackcloth, and went softly to show that his strength was exhausted with sorrow (1 Kings xxi. 27). Isaiah says, I shall go softly all my years in the bitterness of my soul (xxxviii. 15). The Psalmist says, My clothing was sackcloth I walked as [for] a friend
or brother. The French Je vais doncement means precisely the same thing: I go softly, because I am indisposed, out of sorts, or in low spirits.