There was once a Charcoal-burner who lived and worked by himself. A Fuller, however, happened to come and settle in the same neighbourhood; and the Charcoal-burner, having made his acquaintance and finding he was an agreeable sort of fellow, asked him if he would come and share his house. “We shall get to know one another better that way,” he said, “and, beside, our household expenses will be diminished.” The Fuller thanked him, but replied, “I couldn’t think of it, sir: why, everything I take such pains to whiten would be blackened in no time by your charcoal.” (Reference: Aesop’s Fables)

The Bible informs us that light can have no communion with darkness (2 Corinthians 6:14). In other words, holiness can have no communion with sin or that Christ Jesus can have no concord with the devil. We cannot be unequally yoked in our lives. Let us learn to recognize that as the sanctified blood-bought saints of God, we can have nothing to do with evil (sin), for in doing so, we darken our washed lives and place ourselves into the judgment of God, for there remains no more sacrifice for our sins, if we continue to willfully sin, after having received the knowledge of Salvation, found in Christ Jesus alone.(Hebrews 10:26)

Ephesians 5:7-11 (KJV)
7 Be not ye therefore partakers with them.
8 For ye were sometimes darkness, but now are ye light in the Lord: walk as children of light:
9 (For the fruit of the Spirit is in all goodness and righteousness and truth;)
10 Proving what is acceptable unto the Lord.
11 And have no fellowship with the unfruitful works of darkness, but rather reprove them.

2 Corinthians 6:14-17 (KJV)
14 Be ye not unequally yoked together with unbelievers: for what fellowship hath righteousness with unrighteousness? and what communion hath light with darkness?
15 And what concord hath Christ with Belial? or what part hath he that believeth with an infidel?
16 And what agreement hath the temple of God with idols? for ye are the temple of the living God; as God hath said, I will dwell in them, and walk in them; and I will be their God, and they shall be my people.
17 Wherefore come out from among them, and be ye separate, saith the Lord, and touch not the unclean thing; and I will receive you.