Do not be yoked together with unbelievers. For what do righteousness and wickedness have in common? Or what fellowship can light have with darkness? – 2 Corinthians 6:14 NIV
Oxen are yoked together to allow them to pull heavier loads together. But not just any two oxen can be hooked up together. If the animals are not well trained and compatible with each other, if they are unequally yoked, their union together will be less than productive.
And this is what Paul is alluding to here. He is not advocating that believers should not associate with unbelievers. It is important that we do so in order to be the salt and light of the world. Instead he is talking about close relationships such as marriage, business partnerships, and best friends. While these ‘mixed’ relationships may start well, and might be able to function over the long term, the differences in values will cause problems. The believer should be seeking to honor God in all they do. But that is not a concern to the unbeliever who will have different priorities. Inevitably, the believer will be tempted to compromise in order to maintain the relationship. How much better to be in relationships where both partners have the same values and goals and can work toward them together.
Paul clearly directs believers who find themselves married to unbelievers to maintain the relationship (1 Cor. 7:12-16). But if we find that other ‘unequally yoked’ partnerships are causing us to consider compromise, we should give thought to either ending the relationship, or at least reducing the involvement. And be careful about entering into partnerships with unbelievers. It is probably better to miss out on an opportunity than to be faced with the ongoing struggle to compromise your values or integrity.