One thing I have always found puzzling is the purpose of the Jewish dietary laws. In Second Temple Judaism obeying the complex dietary laws was a central religious duty. A lot of time and energy was spent on specifying these laws and on obeying them. These laws, after all, come directly from God. Then after Jesus comes and does his thing, the laws drop out of the new Jewish sect which grows up around the risen Jesus. Jesus, in fact, declares all foods clean in Mark 7:14-19 (also see Acts 10:13-16.) Christians can eat anything. The laws no longer apply. Poof. Gone.
But what is up with that? Why does God demand that his people obey a complex set of laws about what to eat for a thousand years and then suddenly (and almost as an afterthought) abolish them? What was the point of that? What is going on?
Answering this question requires a view that salvation history unfolds in distinct stages. Different rules are appropriate at different stages. The dietary laws are part of the Nation of Israel stage. At this point, God has set aside a chosen people to live apart from the nations and do something new: worship and live in a covenant relationship with the one true God. This is new. The newness requires separation from the nations. If the Hebrews were too involved in the lives of the other nations, then they would be tempted to follow their old ways (which still seem far more natural and normal.) Doing something radically new requires a separation. People who attempt to build ideal communes or who want to live alternative lifestyles find it necessary to separate themselves from the rest of society. The newness of the project demands the separation.
The dietary laws were a mean that God used to keep the Hebrews separate from the surrounding nations. Dietary laws are a pretty good way to do this in fact. One of the most social times of the day (even now) is mealtimes. Who one eats with is an important part of social life. The Jewish dietary laws made it hard for Jews to eat with people of other nations. They had to eat only with other Jews. This fact gave them a certain amount of social separation from the nations even in their intimate lives.
Thus, the dietary laws could even be entirely arbitrary (although I don’t think they were.) Their point was simply to effect a separation any complex set of laws would do this. This also explains why after Jesus the dietary laws no longer apply. After Jesus, the Jewish faith is opened up to all people everywhere. The separation that once existed no longer does. The time is ripe for all people to be invited into the new project of living in a covenant relation with God. Once that time comes, then all of those things which were meant to bring about separation dropout and so all foods become clean.