Brownlow North, the Scottish lay evangelist of the 19th century, has a sermon on this subject in which he calls this sin, the sin of spiritual intermarriage, the worst sin, the most catastrophic sin of all the sins identified in the Bible that can be committed by a Christian man or woman. In his own words: “In reading my Bible I find no sin there recorded, if we except the sin of our first parents, which has brought greater curse upon the earth, or which is more positively forbidden, both in the Old and New Testament” (Wilt Thou Go with This man? p. 112). For, you see, that sin corrupts the stream of believing life and may lead to the damnation of thousands, as it did many times in the Bible.
Robert Rayburn