Sweat Of One's Brow Meaning

(idiomatic) The effort extended in labor, and the value created thereby.

Example: 1922, James Joyce, Ulysses Episode 12, The Cyclops
  So anyhow Terry brought the three pints Joe was standing and begob the sight nearly left my eyes when I saw him land out a quid O, as true as I'm telling you. A goodlooking sovereign.
  --And there's more where that came from, says he.
  --Were you robbing the poorbox, Joe? says I.
  --Sweat of my brow, says Joe. 'Twas the prudent member gave me the wheeze.
1984, Genesis 3:19, New International Version
  By the sweat of your brow you will eat your food until you return to the ground, since from it you were taken; for dust you are and to dust you will return."