Updated January 2022; fist posted February 2019.
Traditional interpretations of Scripture often seem to become Scripture over time. Peter’s vision in Acts 10 is a case in point:
Acts 10:10-15 (CJB)
 He began to feel hungry and wanted something to eat; but while they were preparing the meal, he fell into a trance  in which he saw heaven opened, and something that looked like a large sheet being lowered to the ground by its four corners.  In it were all kinds of four-footed animals, crawling creatures and wild birds.  Then a voice came to him, “Get up, Kefa, slaughter and eat!”  But Kefa said, “No, sir! Absolutely not! I have never eaten food that was unclean or treif.”  The voice spoke to him a second time: “Stop treating as unclean what God has made clean.”
The Hebrew term “treif“, here (literally, “torn”, as if by wild animals or by falling off a cliff), and its Greek equivalent, “koinos“, include any food that is non-kosher, profane (common), defiled, unclean, or unholy.
Most Christian theologians today, would say, “That is an object lesson, but it is also a clear statement that God has cancelled His own commandment!” But did He? First, let’s be clear, the Jewish dietary laws have never applied to non-Jewish believers! Torah was God’s teachings to Jews, His commandments to them to set them apart from the profane ungodly, as His holy people. The closest we have in the New Testament to a dietary commandment for non-Jewish believers, is an opinion delivered by James at the first church council, in Jerusalem:
Acts 15:19 (CJB)
 “Therefore, my opinion is that we should not put obstacles in the way of the Goyim [essentially, Gentiles] who are turning to God.  Instead, we should write them a letter telling them to abstain from things polluted by idols, from fornication, from what is strangled and from blood.
What was Peter’s understanding of his trance? At first, he didn’t get it at all! The voice had to tell him three times, “Stop treating as unclean what God has made clean” (vs 16). Yet, in the following verse, when he awoke from his trance, he “was still puzzling over the meaning of the vision he had seen” (vs 17). Then “While Kefa’s [Peter’s] mind was still on the vision, the Spirit said, “Three men are looking for you” (vs 19).
I think that is when the light dawned for Peter. The sheet was a vision, not a reality. The food on it was a vision. God wanted to teach him something. The vision wasn’t about food, it was about people! He was given an object lesson; the lesson taught him
Acts 10:28 (CJB)
 He said to them, “You are well aware that for a man who is a Jew to have close association with someone who belongs to another people, or to come and visit him, is something that just isn’t done. But God has shown me not to call any person common or unclean…”
Something else needs to be clarified: Peter’s attitude going into this incident was wrong to begin with. There is no commandment in scripture that tells Jews to shun non-Jews! There are only the traditions of the rabbis to account for it. A “cultural construct”. Got created all mankind “clean” from the very beginning. A Gentile in sin is no more defiled than a Jew in sin—in fact because God gave Torah to Israel, He holds them to a higher standard. God doesn’t defile mankind, we defile ourselves. Only God’s grace can restore the holiness we relinquish.