John Calvin Commentary Acts 10:14

"But Peter said, Not so, Lord; for I have never eaten anything that is common and unclean." — Acts 10:14 (ASV)

Not so, Lord. This is the voice of him who both refuses and objects to God His own commandment. He is afraid, for good reasons, to touch what he knew was forbidden to him in the law of God (Leviticus 11:21 and following). Therefore, he objects to God the law which God Himself made, so that he would not break it unintentionally.

There was a certain appearance of inconsistency between the law and the vision; therefore, Peter is not hasty but desires first to have his doubt resolved before he departs from observing the law. Yet it is a strange matter why Peter resisted more regarding food than Abraham did regarding killing his son, for Abraham might have had more things to object (Genesis 22:9–10).

I dare not say here that what happened to Peter is what is too common among people: to be more concerned about outward and trivial matters than about the main points of the law. I rather offer the answer that is beyond doubt: that Abraham’s mind was so convinced, and he was equipped with such power of the Spirit, that he overcame with lofty and heroic fortitude all those things that might have hindered him.

But the Spirit of God worked less powerfully in Peter; from this we are taught that every small or insignificant thing causes us to doubt, unless the Lord furnishes us with wisdom and steadfastness to overcome all fear. Yet Peter acts very godly and very religiously in that, being in doubt amidst various thoughts, he dares to do nothing until it becomes clearer what he ought to follow. Common here means profane.

For the Lord (as we have said) had chosen the Jews to be a special people, He had prescribed to them this rite and way of life, so that it might distinguish them from the profane Gentiles. Therefore, whatever the Gentiles used that was contrary to the rule of the law, that they called common, because there was nothing pure or holy except what God had appointed for the use of His people.