Likutei Halakhot, Yoreh Deah, Laws of Meat and Milk 3:1/ליקוטי הלכות·יורה דעה·הלכות בשר בחלב ג׳:א׳

3And that is the aspect of the prohibition of meat and milk. As even though this is permissible and that is permissible; nevertheless when they are joined together, meat and milk become a forbidden substance. For every item in the world is drawn from the ten utterances through which the world and everything in it was created; and everything was created for His glory, may He be blessed, as mentioned above. But there is a boundary to each and every glory, etc., as mentioned above. And therefore each and every item is different from its fellow in its form and its rationale, etc. It is all according to the boundary of the aspect of glory with which it is clothed. So we very much need to guard the aspect of the boundaries and limitations of each aspect of glory that is clothed in every item, not to break down the boundary, God forbid. For beyond the boundary are the places of the external forces, even with holiness. For it is forbidden to trespass the boundary of one into the boundary of its fellow. For every aspect of glory that is clothed in every item has a boundary according to the aspect of the prohibition of trespassing its boundary to the boundary of another.