So now the apostle delivers the relevant application: ‘Be ye not unequally yoked together with unbelievers.’ It is absolutely right in context.
Now you relate this to truth and falsehood. You bring in just a little falsehood, and the brightness of the light has gone, you have eclipsed it and spoiled it. You have now got a gloomy light. Perhaps you are in a church where some people hold the truth and some people deny it. Well the kind of light you have got is a dim light and an unhappy light, and the full blessing of God cannot be there. If your church believes the gospel and it is linked with a denomination such as the Church of England or the Baptist Union, both of which are now against the truth, where the bishops and the leaders laugh everything to scorn and believe the opposite, you have got the dimmest light. There you are in your little church working away to spread the truth, but you have got a mighty handicap because you are working in a cloud of darkness. You have tried to mix light and darkness together. The unequal yoke applies to churches getting together in close voluntary Christian service with other churches that deny the faith, do not believe the Bible, the redeeming blood of Christ, and the new birth. Never join a church where unbelief or false doctrine is taught. Do not join a church which teaches the truth but joins itself happily to a denomination or to other churches that are against the truth so that there is a mixture.
It applies also to the individual Christian, and yes, it applies to courtship and to approaching marriage. Now in 1 Corinthians 7 the apostle deals with the problem that arises if somebody is converted while married. Two unbelievers have married, now one of them has been converted. Should the believer leave the unbeliever? No, says the apostle, not unless the unbeliever leaves. The task of the unbeliever now – and God is gracious and he will mightily help – is to win the unbelieving spouse. But when it comes to courtship or considering marriage, this is the rule. A believer cannot marry an unbeliever. It is like joining two completely dissimilar animals in the same yoke or harness in ploughing. You cannot be closely joined together with someone whose whole priority is for holiness and obeying the law and his standards with another person who does not share those standards and to some degree will be against those standards.
When we come to the doctrine of separation from false teachers and the regulation included here about the marriage of believers, some people become uneasy. That is because they tend to have been influenced by the prevailing idea in the world – no one is ever wrong. This is what fortifies the ecumenical movement.