But it is to be observed that the Jews, who claim for themselves a correct understanding of the law of Moses, carefully restrict their food to such things as are accounted clean, and abstain from those that are unclean. They also do not use in their food the blood of an animal nor the flesh of an animal torn by wild beasts, and some other things which it would take too long for us at present to detail. But Jesus, wishing to lead all men by His teaching to the pure worship and service of God, and anxious not to throw any hindrance in the way of many who might be benefited by Christianity, through the imposition of a burdensome code of rules in regard to food, has laid it down, that “not that which goes into the mouth defiles a man, but that which comes out of the mouth; for whatsoever enters in at the mouth goes into the belly, and is cast out into the draught.
But those things which proceed out of the mouth are evil thoughts when spoken, murders, adulteries, fornications, thefts, false witness, blasphemies.” Paul also says, “Meat commends us not to God: for neither, if we eat, are we the better; neither, if we eat not, are we the worse.” Wherefore, as there is some obscurity about this matter, without some explanation is given, it seemed good to the apostles of Jesus and the elders assembled together at Antioch, and also, as they themselves say, to the Holy Spirit, to write a letter to the Gentile believers, forbidding them to partake of those things from which alone they say it is necessary to abstain, namely, “things offered to idols, things strangled, and blood.”
Source: Against Celsus (New Advent)