I would like to claim that God is consistent in everything but I wonder why an eternal God outside of time would use pretty strong language such as “detestable” and “unclean” denouncing certain foods (Leviticus 11) and then decide to change it and say everything is clean (Acts 10) in the New Testament. Why have certain foods that are clean and unclean (red kite, bats, pork etc) if they were all clean in the first place? And if the moment they became clean was when Jesus said it was clean, why call it dirty? Am I to just accept that sometimes He changes his mind? I don’t know how to harmonize this with the strong language on how unclean the food actually was to God.
A similar example is Exodus 32: 13 Remember Abraham, Isaac, and Israel, thy servants, to whom thou swarest by thine own self, and saidst unto them, I will multiply your seed as the stars of heaven, and all this land that I have spoken of will I give unto your seed, and they shall inherit it for ever. 14 And the Lord repented of the evil which he thought to do unto his people. Verse 14 seems to imply the God has to forgive Himself for wanting to break his convenant with Abraham. If He is an all knowing God when he made a promise and knew the people would have little faith, why this internal struggle with keeping his covenant? Is the only logical conclusion that God does not know how we will choose or how faithless we would actually be? Do we have to remind God of some of the promises He gave us like His promise to give us peace?
In Leviticus 11 God says to his people that certain kinds of meat are “unclean for you.” He also says that some meats “you are to detest.” God does not tell the people that the food itself is detestable, but that for them, it would make them (ceremonially) unclean. Because this kind of food made them ceremonially unclean, God told them to detest the food which made them unclean. I cannot say for sure exactly why God chose these particular kinds of meat (carnivores, shellfish, pork, etc.). However, it just so happens that the kinds of meat God said they could eat are relatively safe to eat and the kinds he told them to consider unclean are relatively unclean in terms of causing disease. Beef is relative safe for human consumption, even if raw, as is fish with scales, whereas pork carries many dangerous diseases for humans and shellfish is also relatively dangerous, as are the meat of carnivores. I cannot prove that God told the Jews not to eat this food because it would make them healthier, but this seems a very reasonable explanation. God told the Jews that if they would keep his laws they would have “none of the diseases” of their neighbors (Exodus 15:26). When the Jews obeyed God in the kind of meat to eat, many of thousands of lives were saved.
One can argue that the surprising thing is that Jesus declared these meats clean for Christians. Why, if they are relatively dangerous for us to eat, did God not keep these prohibitions for Christians. I believe that there are a couple of possible reasons for the change. First of all, the “laws” in the New Testament are generally spiritual, whereas they are more physical, in general, in the Old Testament. We are to avoid spiritual uncleanness, rather than ceremonial uncleanness. A second reason is that, with Christianity spreading throughout the earth, with thousands of languages and cultures, God decided that such rules were not practical. The simpler the “rules” were for Christianity as it spread, the more easily the gospel could spread. I can neither prove that God outlawed these kinds of meats because of the health danger, nor prove that he removed this prohibition for practical reasons as the gospel spread to many peoples, but this is my best guess. Eating certain meats are not sinful (spiritually unclean), per se, but were only outlawed for practical reasons of health, so I believe this is a reasonable explanation. Either way, I do not believe that God changed his mind, but that, in his wisdom, different laws applied in different situations. Lying, stealing, murder and so forth are inherently evil, but eating certain kinds of meat is not inherently sinful.
As for Exodus 32:13-14, the fact that you are using the antiquated King James version is a contributing factor to the question. A more modern translation, the NIV, has Then the Lord relented and did not bring on his people the disaster he had threatened (Exodus 32:14). There are many examples in the Bible where God told his people that if they did not repent, he would bring disaster on them, but that if they did repent, he would relent, and bring them blessings instead. Deuteronomy 28 and 29 is a long passages which describes blessings and curses God would bring on his people if they obeyed him or rebelled against him. I believe that Exodus 32:13-14 is an example of this principle that God will either judge or bless his people, depending on their willingness to obey him. It is not God who is changing his mind, but it is his people who change their minds and bring about a change in how God deals with his people. A similar idea applies to the Ninevites to whom Jonah preached. God had Jonah preach judgment, but because the Ninevites repented, God decided to not judge them.
I understand that it can be a bit confusing when we think about the fact that God, in his omniscience, knows what we will do, but he treats us as if he did not know what we will do. If I understand God correctly, he foreknows what we will do, but does not predetermine what we will do. He gives us “free will.” To the extent that we have free will, God allows our decisions to determine what his actions will be toward us. Again, for humans for whom time is a linear thing, this is hard to understand, but God speaks to us in human terms because we are human. I believe this explains the language in a passage like Exodus 32:13-14.