In this passage, we should remind ourselves that context is vital in our understanding of what Paul is stating. There are three ideas which he puts across, two specific to the age in which he lived, one for all time.
1. When a sacrifice was offered, part of the meat was given back to the worshipper to hold a feast and at these feasts it was taken that the god was a guest there. It was even assumed that the god was in the meat which was offered as a sacrifice and so, by eating the meat, those at the feast would experience the presence of the god in their bodies! A sacrificial meal formed a real communion between worshipper and god.
2. In Paul's day, the whole world believed in demons, more often these were bad demons. I remember travelling through parts of India and seeing people worshipping trees, the whole of nature alive with spirits. Paul termed these demons, 'principalities and powers'. Those who worshipped to gods believed they were communing with the god, but in reality they were coming into contact with demons.
3. Out of these ancient beliefs comes one permanent principle: men and women who sat at the table of Jesus Christ in Communion could not go and sit at the table which the demons are using as their instrument. When we handle the body and blood of Jesus we are committed to a road of holiness, being set apart.
This principle is for us to work out in our daily lives. the idea that we might consciously sit and eat with those who had sacrificed that food to an idol is highly unusual in the UK context, but there are other things we may do which put us on the pathway to being swallowed up by evil. I have learned that there are places I cannot go and people I cannot get involved with, because of the potential of being led astray. That doesn't mean that I remain aloof from everyone, it just means as Paul wrote in verse 13 that God will provide a way out of temptation, but don't make a mockery of Him and use His gift of grace cynically!