(The ). Conscience, or the soul of man. The Mahometans have preserved the old Roman idea in the doctrine that the souls of the just lie under the throne of God, like white birds, till the resurrection morn.
“A white bird, she told him once ... he must carry on his
bosom across a crowded public place—his own soul was like
White Brethren or White-clad Brethren. A sect in the beginning of the fifteenth century. Mosheim says (bk. ii. p. 2, chap. v.) a certain priest came from the Alps, clad in white, with an immense concourse of followers all dressed in white linen also. They marched through several provinces, following a cross borne by their leader. Boniface X. ordered their leader to be burnt, and the multitude dispersed.
Source: Dictionary of Phrase and Fable, E. Cobham Brewer, 1894
More on White Bird from Fact Monster: