The Emerald Tablet is extremely short, a dozen or so numbered sentences depending on the recension, and almost every one of them has been the subject of centuries of commentary. It contains the line usually given in English as as above, so below, which has become the most quoted sentence in Western esotericism and which in the original is a statement about correspondence between what is above and what is below for the accomplishing of the miracle of one thing.
What the tablet was actually used for is more specific than its modern reputation suggests. Alchemists read it as a veiled recipe: a compressed account of the stages of the Work, with the separation of earth from fire, the ascent and descent, and the acquisition of the glory of the whole world read as operations to be performed rather than as metaphysics to be contemplated. Dozens of commentaries survive that take it exactly that way, matching each sentence to a laboratory stage.
Isaac Newton made his own English translation of it, in a manuscript that stayed unpublished for centuries, which is a useful corrective to the idea that the alchemical and the scientific are separate lineages that never touched.
Its brevity is part of its function. A text of a dozen sentences can be memorised, carried without a book, and set at the head of a longer work as an epigraph, and the Emerald Tablet has been used all three ways.