John Chrysostom
Cornelius was uncircumcised and had nothing in common with the Jews. Therefore, since Peter had in view that everyone would accuse him as a transgressor of the Law, and this mattered greatly among them, he is necessarily disposed to say, "I have never eaten."
He did not arouse this concern in himself. No. As I have said, he was disposed to this by the Spirit. Thus, in answer to his accusers, he would have as his defense that he had even objected.
They were very zealous about observing the Law. He was being sent to the Gentiles. Therefore, as I said above, this happens so that the Jews would not accuse him.
And so that it would not seem to be some apparition, he said, "No, Lord; I have never eaten anything common or unclean."
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Why, they will say, did he object? So that no one might say that God was testing him, as He tested Abraham when He commanded him to sacrifice his son.
Or as He tested Philip when Christ asked him, "How many loaves do you have?" (Mk 6:38). He did not ask in order to learn this, but to test him (Jn 6:5).
Moreover, in the Law Moses separately indicated the clean and the unclean, both among land creatures and sea creatures. Yet Peter did not understand this.
Why, then, did such an event take place? For the generations that followed, to whom it would be told. And Peter himself had heard the command, "Do not go into the way of the Gentiles" (Mt 10:5).
Do not marvel at this. If Paul considered circumcision and sacrifices necessary, then they seemed still more necessary at that time, at the beginning of the preaching, when there were still weaker believers.