πᾶν ὃ δίδωσί μοι ὁ πατὴρ πρὸς ἐμὲ ἥξει· καὶ τὸν ἐρχόμενον πρός με οὐ μὴ ἐκβάλω ἔξω. (John 6:37)
All that the Father giveth me shall come to me; and him that cometh to me I will in no wise cast out. (John 6:37)
Here is a very simple lesson in Greek. In the Greek New Testament there are two words for, “no”: οὐ (“oo” as in shoe) and μη (“mey”). The difference between the two negatives is found in the Greek Lexicons,
ΜΉ, not, is the negative of thought, as οὐ of statement, i.e. μή says that one thinks a thing is not, οὐ that it is not. The same differences hold for all compds. of μή and οὐ. 
Each of the two negatives are used differently, BUT when combined together as οὐ μὴ, it carries with it the strongest form of a negative possible in the Greek.
John 6:37 says that if anyone comes to Christ he will in “no wise” reject him. When the Bible says “no wise”, the words being used are οὐ μὴ. It is very clear. If you are truly saved you will NEVER EVER lose your salvation. God is the one who keeps you (John 10:28-29) and you are sealed with God’s Holy Spirit until you are completely redeemed (Ephesians 1:13). Anyone who has an argument with this is not opposing me, but the very Word of God.
 H.G. Liddell, A Lexicon : Abridged from Liddell and Scott’s Greek-English Lexicon (Oak Harbor, WA: Logos Research Systems, Inc., 1996). 507.