2 Corinthians 6:14

Be ye not unequally yoked together with unbelievers,.... This seems to be an allusion to the law in Deuteronomy 22:10 and to be a mystical explanation of it; and is to be understood not as forbidding civil society and converse with unbelievers; for this is impracticable, then must believers needs go out of the world; this the many natural and civil relations subsisting among men make absolutely necessary; and in many cases is both lawful and laudable, especially when there is any opportunity or likelihood of doing them any service in a spiritual way: not is it to be understood as dehorting from entering into marriage contracts with such persons; for such marriages the apostle, in his former epistle, had allowed to be lawful, and what ought to be abode by; though believers would do well carefully to avoid such an unequal yoke, since oftentimes they are hereby exposed to many snares, temptations, distresses, and sorrows, which generally more or less follow hereon: but there is nothing in the text or context that lead to such an interpretation; rather, if any particular thing is referred to, it is to joining with unbelievers in acts of idolatry; since one of the apostle's arguments to dissuade from being unequally yoked with unbelievers is, "what agreement hath the temple of God with idols?" and from the foregoing epistle it looks as if some in this church had joined with them in such practices; see 1 Corinthians 10:14. But I rather think that these words are a dissuasive in general, from having any fellowship with unbelievers in anything sinful and criminal, whether in worship or in conversation:

for what fellowship hath righteousness with unrighteousness? This, with what is said in the following verse, and in the beginning of the next to that, contain reasons or arguments engaging believers to attend to the exhortation given not to keep company with unbelievers. By "righteousness" is meant righteous persons, who are made the righteousness of God in Christ, to whom Christ is made righteousness, or to whom the righteousness of Christ is imputed for justification; and who also have principles of grace and holiness in their hearts, or have the kingdom of God in them, which consists of righteousness, peace, and joy in the Holy Ghost; and who being made free from the dominion of sin, are become servants of righteousness: and by unrighteousness is designed unrighteous persons, who are destitute of a justifying righteousness, are filled with all unrighteousness, and are, as it were, a mass and lump of iniquity; now, what fellowship can there be between persons of such distant characters?

And what communion hath light with darkness? regenerate men are made light in the Lord; they are enlightened into their state and condition by nature, to see the exceeding sinfulness of sin, to behold the glory, beauty, fulness, and suitableness of Christ, so as to be sensible of their need of him, and to be able to look unto him for life and salvation; they are enlightened more or less into the doctrines of the Gospel, and the duties of religion; and their path is a shining light, shining more and more unto the perfect day. Unregenerate persons are "darkness" itself; they are dark and ignorant of God in Christ, of the way of salvation by Christ, of the work of the Spirit of God upon the heart, and of the mysteries of grace; they know not themselves, nor the sad estate they are in; they are born, and brought up in darkness worse than Egyptian darkness; they go on in it, and if grace prevent not, will be cast into utter and eternal darkness. Now, what "communion" can there be between persons so different one from another? for what is more so than light and darkness? these the God of nature has divided from each other; and they are in nature irreconcilable to one another, and so they are in grace.