Easton's Bible Dictionary: M. G. Easton, M.A., D.D.
The flesh in various ways was an idolatrous practice, a part of idol-worship (Dt. 14:1; 1 Ki. 18:28). The Israelites were commanded not to imitate this practice (Lev. 19:28, 21:5; Dt. 14:1). The tearing of the flesh from grief and anguish of spirit in mourning for the dead was regarded as a mark of affection (Jer. 16:6, 41:5, 48:37).
Allusions are made in Revelation (Rev. 13:16, 17:5, 19:20) to the practice of printing marks on the body, to indicate allegiance to a deity. We find also references to it, through in a different direction, by Paul (Gal. 6:17) and by Ezekiel (Ezek. 9:4).