We know a thing when we understand it; and we understand it when we can interpret or tell what it signifies. Strictly, the sense knows nothing. We perceive indeed sounds by hearing, and characters by sight; but we are not therefore said to understand them. After the same manner, the phenomena of nature are alike visible to all; but all have not alike learned the connexion of natural things, or understand what they signify, or know how to vaticinate by them. There is no question, saith Socrates in Theaeteto, concerning that which is agreeable to each person, but concerning what will in time to come be agreeable, of which all men are not equally judges. He who foreknoweth what will be in every kind is the wisest. According to Socrates, you and the cook may judge of a dish on the table equaly well, but while the dish is making, the cook can better foretell what will ensue from this or that manner of composing it. Nor is this manner of reasoning confined only to morals or politics, but extends also to natural science. (Berkeley, Siris 253)
That natural science is a sort of sophisticated augury or omen-reading is a common theme in Siris. Compare 252:
There is a certain analogy, constancy, and uniformity in the phenomena or appearances of nature, which are a foundation for general rules: and these are a grammar for the understanding of nature, or that series of efects in teh visible world whereby we are enabled to foresee what will come to pass in the natural course of things. Plotinus observes, in his third Ennead, tha thte art of presaging is in some sort the reading of natural letters denoting order, and that so far forth as analogy obtains in the universe, there may be vaticination. And in reality, he that foretells the motions of the planets, or the effects of medicines, or the result of chemical or mechanical experiments, may be said to do it by natural vaticination.
Berkeley means to be taken literally when he talks about the "grammar for the understanding of nature"; he considers our sensory impressions to be literally linguistic in nature.