Water represents true ideas about day-to-day life, and other drinks and liquids in general represent different forms of truth. Milk is a drink that contains fat, and fat represents the highest human love: the love of the Lord. Because of the fat, milk represents the true ideas that flow naturally from the love of the Lord. This is not something most of us experience, because most of us are caught up in a battle between our selfish desires and our good ones. Because of that, we need to really look for what is true and use that to figure out how to be good; we're led by ideas in our minds. But people -- or angels -- who are in a state of love to the Lord have no such struggles. They know what's right and wrong automatically, based on whether ideas fit their love or not. That kind of truth -- the truth that comes from love -- is represented by milk.