‘ Do not be unequally yoked with unbelievers, for what fellowship have righteousness and iniquity? or what communion has light with darkness? And what concord has Christ with Belial? or what portion has a believer with an unbeliever?'
The problem is that they are having too close a relationship with secular things and those who are not believers. Instead of being properly yoked together as fellow-workers together with God they are unequally yoked together with what is incompatible with their faith. This comes out in the way that they are willing to tie their lives in with the ways of unbelievers in a binding way, in marriage to unbelivers and too close association with idolaters, without thought for the long term consequences. This helps to explain their lack of affection for Paul and for Christ. Their unequal yokes are preventing the enlargement of their affections towards what is right.
For the Christian there is always a fine line between keeping in touch with the world and its ways, and being sucked in by it. Keeping in touch is fine (1 Corinthians 5:10), but becoming obligated to it and having too close an association with it is folly. Thus he warns them about tying themselves in with unbelievers, whether by marriage, binding partnerships, or any kind of commitment that might restrict them in their Christian lives and witness. This includes putting themselves in a position where the course of their life can be determined by others who have secular rather than heavenly aims. In view of the strength of the comparisons that follow (iniquity, darkness, Belial, idols) we must probably see this as very much having in mind certain idolatrous associations, whether the participating in sacral meals in heathen temples, being members of trade guilds where acknowledgement of idols was necessary, or membership in some other such organisation, and even sexual misbehaviour through Temple liaisons. (It is tempting to think that there may have been an association or guild which connected itself with Belial or a god who could be paralleled with Belial).
‘Unequally yoked.' Let them consider that it is important that when two animals are yoked together they be compatible. If they are not the result will do grave harm to the task in hand. For example an ox and a donkey will not make good yoke-fellows (Deuteronomy 22:10), and will wreck any attempts to achieve anything through such a compromise. In the same way Christians must not yoke themselves with those with whom they do not fit spiritually, those who have different aims, or who wish to go in a different direction, or whose methods might result in compromise. For under a yoke, either both are aiming for the same thing, or compromise is inevitable, and if they are yoked to unbelievers that is the road to disaster.
We can compare, for example, how he had reprimanded them for allowing their legal disputes with one another to be arbitrated by the secular courts ("in front of unbelievers," (1 Corinthians 6:1-6). How he had admonished them for joining with pagans in their cultic meals with the resulting compromise of loyalties (1 Corinthians 10:6-22). How he had had to rebuke them for approving of sexual unions with prostitutes, possibly cultic prostitutes (1 Corinthians 6:12-20). These and other such activities are in mind here.
He then applies this more specifically to their situation as Christians (and more specifically to ours). ‘For what fellowship have righteousness and iniquity? or what communion has light with darkness? And what concord has Christ with Belial? or what portion has a believer with an unbeliever'
‘For what fellowship have righteousness and iniquity?' How can those who seek to walk in righteousness with God, and have ‘become the righteousness of God' (2 Corinthians 5:21), live lives in common with, or associate closely with, those whose hearts are set on iniquity, on inward thoughts of evil? Righteousness and sin do not go together. One or the other will soon have to give way, for they are totally incompatible. There can be no compromise with sin. Yet those who are yoked to sinners will find themselves constantly having to do exactly that.
‘What communion has light with darkness?' Again light and darkness are totally incompatible. Introduce light and away goes darkness. Thus both will have to live in semi-darkness. Neither will be comfortable. This is true whether it be the light of Christ in contrast to the darkness of unbelief and sin (John 3:19-21), or the light of righteous living (Matthew 5:16) in contrast with the darkness of selfishness and self-seeking (Matthew 6:22-23). For we who are Christians have been made partakers of the inheritance of the saints in light, and have been delivered from the power of darkness (Colossian 2 Corinthians 1:12-13). How then can we return to the dark? Consider also Romans 13:12 where the armour of light is in contrast to the works of darkness, stressing their incompatibility; 1 Thessalonians 5:5; Ephesians 5:8; Ephesians 5:11-14; Colossians.
‘And what concord has Christ with Belial?' Here is the greatest contrast of all. Christ and Belial are totally incompatible. Belial is probably another name for Satan and in the Old Testament (where it is not a synonym for Satan) represents the ideas of worthlessness, rebellion, evil and lawlessness. See especially 1 Samuel 2:12, where the ‘sons of Belial' contrast with the idea of knowing ‘the Lord' by showing their disobedience to Him.
But the most significant reference is in 2 Chronicles 13:7, where the ‘sons of Belial' having rebelled against the house of David, and therefore against God's anointed (christos), chose to look to the golden calves, thus being divisive, and bringing about the great divide between Israel and Judah. This example alone might be seen as justifying the comparison, and explain Paul's use of it here, for it fits exactly. The ‘sons of Belial' reject the anointed one of God, and destroyed the unity of God's people by consorting with idolatry. In contrast those who are Christ's rejoice in God's Anointed, and in Him are thus again one united people. So they must choose which they will follow, Christ or Belial.
But in intertestamental literature, especially at Qumran, Belial had become a personal enemy of God, prince of demons and possibly a synonym for Satan, which would give deeper significance to the above references. And it may well be that such an idea was known in Corinth, possibly through Judaisers, otherwise why use it in this letter? (Paul may even have been termed by them a ‘son of Belial', drawing out his sarcastic comment that Satan has fashioned himself into an angel of light - 2 Corinthians 11:14).