Why is mating different animals a sin or mixing fields and clothing material?


“Keep my decrees.
“Do not mate different kinds of animals.
“Do not plant your field with two kinds of seed.
“Do not wear clothing woven of two kinds of material.” Leviticus 19:19
“‘You must therefore make a distinction between clean and unclean animals and between unclean and clean birds. Do not defile yourselves by any animal or bird or anything that moves along the ground—those that I have set apart as unclean for you. You are to be holy to me because I, the Lord, am holy, and I have set you apart from the nations to be my own.  Leviticus 20:25-26
            Some of these things seem very petty, like mixing cotton and linen or planting tomatoes and cucumbers, but the point went beyond that.  God wanted the lives of the Israelites to be distinct, pure, separated from the clean and unclean.  They were to be a holy nation, set apart from the others, with practices that emphasized and highlighted their separation.
            That theme of separation extended to their flocks, fields and clothing.  It was meant to remind them of who they were and how they were to act.