II Corinthians 6:11-15

O Corinthians! We have spoken openly to you, our heart is wide open. You are not restricted by us, but you are restricted by your own affections. Now in return for the same (I speak as to children), you also be open. Do not be unequally yoked together with unbelievers. For what fellowship has righteousness with lawlessness? And what communion has light with darkness? And what accord has Christ with Belial? Or what part has a believer with an unbeliever?