Acts 11:9

But the voice answered a second time from heaven, “What God has cleansed you must not call common.”

Peter had definite ideas about what was clean and unclean.  He’d learned them from God himself in the law of Moses, so he figured he was on pretty solid ground.  But then God did something unexpected: he staged a major-league paradigm shift.  God declared to Peter that as contractor of the universe, it was his job, not Peter’s, to decide what was essential and what was not essential in building himself a House.  Long ago, he had laid down a rule about keeping separate from Gentiles and not eating unclean food.  Peter had assumed this was a Rule for All Eternity since the God of eternity gave it.  Now it turned out that this rule was something more like a plywood concrete form.  When a contractor builds a plywood concrete form he intends it to be secure, but temporary.  Once the concrete he has poured into the form is dry, the form goes.  Once the New Covenant was dry, the temporary barriers God had erected between the Jewish members of his House and the Gentiles he was now bringing in also went.  And so, Peter came to realize that God “made no distinction between us [the Jews] and them [the Gentiles], but cleansed their hearts by faith” (Acts 15:9).  The temporary had passed.  The Eternal was now here.