Why is it that Peter would not dream of eating unclean foods? Because his scriptures told him it was not ok. Leviticus 11 spells out clearly what foods are clean and what foods are unclean. And observant Jews to this day follow that scripture.
Peter’s vision told him that the revelation of God had not ended with Leviticus. It was continuing with Jesus. The scriptures, his scriptures, could be set aside if they got in the way of the continuing revelation of God in Jesus. The scriptures said it then, but now we see differently.
It is this same insight that has set the movement free throughout history to get beyond what it says in the Bible. The Bible said that slavery was ok; the Bible said that women should be subjugated to men. The Bible says that divorce is wrong and that divorced people and re-married people cannot participate fully in the life of the church as leaders. But fortunately at key moments in history some visionaries have seen the continuing unfolding of God’s revelation to include everybody and anybody who wants to be a part of the movement and not to allow what the Bible says to get in the way of God speaking to us today with a new vision.
And of course the Bibles says that homosexuality is an abomination. Well, it doesn’t actually say that but lots of Christians think it does. But it doesn’t matter because what the scripture writers knew about sexuality is not what we know. We see and know differently today. And we can say with confidence that God wants us to accept and welcome gays into our community. And we learned that from Peter's dream.