It might seem odd for someone with a Hebrew Bible background to begin their first real theological post in the New Testament, but as often might be the case for Christians who spend time in the Old Testament, you begin to see familiar passages from a different angle and with richer meaning. In this case, the familiar passage of Peter's vision in Acts 10, which is given to justify Peter's evangelism to Gentiles, makes a peculiar (and seemingly dangerous) argument: That God can change the rules.
But does he change the rules? Peter certainly thinks so. The vision occurs three times because of Peter's reluctance to change what he thought was the correct application of a set of laws, particularly Lev. 11:2-47. To be clear, not all "four-footed animals," nor all birds, nor all "creeping things of the ground" are forbidden, but subsets of each of these are. What makes this verse and passage interesting hangs on the use of πάντα in v. 12 - "all kinds." To be fair, I haven't consulted any commentaries or journal articles on this as of yet and am purely working from the Greek, but this is a different scenario than I've traditionally heard preached, which implies that God is calling Peter to eat pigs, rats, salamanders, and crawdads. However, if it is understood that only subsets of each of these groups are forbidden, it means that in Peter's "piousness," he has taken a personal ban of eating anything from these groups, banned or not.
Why? There is an interesting wordplay in this passage that offers some explanation. Depending on your translation of v. 14, you might read Peter saying that he hasn't eaten anything "defiled" (NET), "unholy" (NASB), "impure" (NIV) or unclean (ἀκάθαρτος). ESV has the literal translation of "common" (κοινὸς). This word, "common," is used elsewhere in the New Testament without any sense of meaning "unholy" or "impure." Instead it's rendered as "common salvation" or "common faith" (Tit 1:4, Jude1:3, Eph 4:4-6, cf. ISBE, "common"). In these cases, "common" is used positively.
There is another nuance which may shed some light here. The generic Hebrew word for a nation, גוי, is often rendered as the Greek, εθνος, in translation. In the most base sense of the words, they are matter-of-fact and not derogatory. God promises to make Abraham into a great גוי (Gen 12:2) and bless him. However, the same words in a different context are used to mean "Gentile." In other words, it no longer means simply "nation," but another nation. A different nation. And taken all the way: a person of a people who does not belong to "us."
You might rightly ask me why I've introduced a word that's not being used in this passage. It turns out that this very usage is the key to understanding what's going on with Peter: All of these animals are "common." They're what everyone else eats, except us. Holiness was defined for Peter by what he did not eat, and it was a source of pride and his identity that he went above and beyond the prohibitions. He didn't just forgo pigs, but beef. He didn't just forgo owls, but chicken, too. Yet now God was calling him to do something that required eating chicken.
The response from God is clear: ἃ ὁ θεὸς ἐκαθάρισεν, σὺ μὴ κοίνου. What God has purified, you are not to [call] common. God is using the same nuance and turning it back around on Peter. Peter, in his pious overregulation, was actually at odds with God. Peter believed that God was tempting him to do something profane, yet the real profanity was Peter's own contrived meaning of holiness.
Since holiness for Peter meant that he was part of an elite, uncommon group, he did not want to give up that status for himself. We know from the story that this wasn't even about dietary laws, but that Peter was treating food the same way as he was people. God wanted Cornelius, a gentile - someone "common." God wanted Peter to bring a fried chicken and burgers to his next ultra-holy club group meeting and serve them alongside all the other dishes. The beauty of the story for Peter is that he found that true Holiness means being in God's will. Instead of spending his time worrying about chicken and burgers, he got to see the Holy Spirit poured out on Cornelius and others who Peter would have called simply "common."
There is one other place in the New Testament where "common" and the issue of purity is raised. In Mark 7:14-23, Jesus distinguishes that it is the character of the person that makes him clean or unclean, not the food itself. Much like the case in Acts 10, Jesus is emphasizing that the token definition of holiness offered by extraneous rules is empty when the same people who refuse to eat chicken are the same who treat others violently, unfairly, and unjustly. Jesus doesn't even mention "common," but the end of v. 19 is a parenthetical by the author that shows that this teaching had weight on how the early church wrestled with how to deal with Torah dietary laws and is aside from Jesus' main point.
Holiness is not achieved by token displays of being different from others in dress, diet, or anything superficial, but holiness instead flows from being in the will of God and treating others around you justly. It is natural that true holiness should then inform such things as dress and diet, but it is an outcome rather than a definition.
There are two prominent Holiness teachers who endured similar lessons to Peter. AB Simpson, the founder of the Christian and Missionary Alliance, was a well-paid pastor of a prestigious church in New York. After reading literature from the Deeper Life Movement, he felt convicted that he needed to minister to the poor and spent his time among immigrants coming into New York. When they started coming to his church, it made the affluent parishioners uncomfortable, so he decided to leave his lofty post and continue his calling for ministering to the poor. His subsequent work was a great success during the Missions movement and beyond.
John Wesley, himself, is the other example. The early Methodists were a somewhat diverse spread, including many who were Reformed (a contingent remaining to this day). John Wesley's friend George Whitefield, who encouraged John in the "open-air" preaching, which would define the early strategy of spreading Methodism via itinerant circuit-riders, was himself Reformed. Though Wesley may have had some endearing things to say about Calvin at times, the issue of predestination became a schismatic wedge between Wesley and Whitefield and their respective followers. Toward the end of his life, Wesley in his sermon, A Caution Against Bigotry, wrote:
But be not content with not forbidding any that casts out devils. It is well to go thus far; but do not stop here. If you will avoid all bigotry, go on. In every instance of this kind, whatever the instrument be, acknowledge the finger of God. And not only acknowledge, but rejoice in his work, and praise his name with thanksgiving. Encourage whomsoever God is pleased to employ, to give himself wholly up thereto. Speak well of him wheresoever you are; defend his character and his mission. Enlarge, as far as you can, his sphere of action; show him all kindness in word and deed; and cease not to cry to God in his behalf, that he may save both himself and them that hear him.
Wesley, like Peter, had learned not to call fellow believers, whom God has purified, merely "common."