6:14 yoked together. Paul is using a metaphor here based on Deuteronomy 22:10 and Leviticus 19:19, which forbade plowing with an ox and ass yoked together, or attempting to interbreed animals of different kinds. The clear inference is that believers and unbelievers are so different in character and interests (as well as ultimate destiny) that they should never be “yoked” together in situations requiring strong agreement of attitudes and goals (e.g., marriage, churches, business partnerships, lodges or other organizations with religious overtones). The prohibition is not intended to require complete repudiation of all secular or charitable organizations (note I Corinthians 5:10) or friendships. When one’s Christian faith is in jeopardy, or his Christian conduct and influence is endangered, then such connections should be severed. One can witness to unbelievers without partaking of their beliefs or sinful behavior.

6:15 concord. The Greek word for “concord” (sumphonesis) is the word from which we get “symphony.”

6:16 God hath said. See Leviticus 26:11-12 and Ezekiel 37:26-27.

6:17 saith the Lord. See Isaiah 52:11. Note also the command to come out of “Babylon” Jeremiah 51:45; Revelation 18:4).

6:18 my sons and daughters. This promise is not quoted explicitly from any Old Testament passage, though the sense of it can often be detected. There are also many explicit New Testament passages that do assert that those who receive Christ become children of God (e.g., John 1:12; Romans 8:16). By direct inspiration, if nothing else, Paul could assure his readers that being separated unto God from the world, through receiving Christ, would indeed assure them that He would receive them as His sons and daughters.