I noticed in my Greek New Testament last night that Galatians 5:16 uses “οὐ μή” when it says, “This I say then, Walk in the Spirit, and ye shall not [“οὐ μή”] fulfil the lust of the flesh.” I thought it was interesting that it used both “οὐ” and “μή” because either one on its own would mean not (1Jo 2:4 uses only μή and 1 John 3:9 uses only οὐ). I thought, “I wonder if it uses both for emphasis, to make it a more emphatic denial?”
I looked it up just now and strong said:
“οὐ μή ou mḗ, oo may; i.e. G3756 and G3361; a double negative strengthening the denial; not at all:—any more, at all, by any (no) means, neither, never, no (at all), in no case (wise), nor ever, not (at all, in any wise).”
And Thayer’s said:
“The participle of οὐ μή in combination augments the force of the negation, and signify not at all, in no wise, by no means.”
This is a great argument for Christian Holiness, that those who are actually walking by the Spirit will absolutely not live a sinful life.
~ Jesse Morrell
http://www.OpenAirOutreach.com
Biblical Truth Resources 
“Then spake Jesus again unto them, saying, I am the light of the world: he that followeth me shall not [οὐ μή] walk in darkness, but shall have the light of life.” John 8:12