1 Timothy 4:3
Any thing taught contrary to God's word is a doctrine of the devil. St Paul was telling Timothy that those forbidding marriage and eating of meats were teaching the doctrines of the devil.
What and when and how to eat is a devils doctrine in the new covenant because Jesus has declared all foods to be eaten. There is nothing that goes on the inside that makes a person unclean except what comes out of the mouth. The heart condition is what decides the flow of our words and this is why any teaching contrary to God's word is to be rejected and ignored.

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