Below is Thomas Taylor's English translation of this key text from the Latin "paraphrase" of Marsilio Ficino entitled by him, De Sacrificio et Magia. For a more accurate translation from the Greek text (as edited by Joseph Bidez in the Catalogue des manuscrits alchimiques Grecs VI ) see Stephen Ronan's translation (offsite link) at his superb site.

Περι της ἱερατικης τεχνης - Peri tês hieratikês technês

In the same manner as lovers gradually advance from that beauty which is apparent in sensible forms, to that which is divine; so the ancient priests, when they considered that there is a certain alliance and sympathy in natural things to each other, and of things manifest to occult powers, and discovered that all things subsist in all, they fabricated a sacred science from this mutual sympathy and similarity. Thus they recognized things supreme in such as are subordinate, and the subordinate in the supreme; in the celestial regions, terrene properties subsisting in a causal and celestial manner; and in earth celestial properties, but according to a terrene condition. For how shall we account for those plants called heliotropes, that is, attendants on the sun, moving in correspondence with the revolution of its orb, but selenitropes, or attendants on the moon, turning in exact conformity to her motion? It is because all things pray, and hymn the leaders of their respective orders; but some intellectually, and others rationally; some in a natural, and others after a sensible, manner. Hence the sunflower, as far as it is able, moves in a circular dance towards the sun; so that if any one could hear the pulsations made by its circuit in the air, he would perceive something composed by a sound of this kind, in honour of its king, such as a plant is capable of framing. Hence, too, we may behold the sun and moon in the earth, but according to a terrene quality; but in the celestial regions, all plants, and stones, and animals, possessing an intellectual life according to a celestial nature. Now the ancients, having contemplated this mutual sympathy of things applied for occult purposes, both celestial and terrene natures, by means of which, through a certain similitude, they deduced divine virtues into this inferior abode. For, indeed, similitude itself is a sufficient cause of binding things together in union and consent. Thus, if a piece of paper is heated, and afterwards placed near a lamp, though it does not touch the fire, the paper will be suddenly inflamed, and the flame will descend from the superior to the inferior parts. This heated paper we may compare to a certain relation of inferiors to superiors; and its approximation to the lamp, to opportune use of things according to time, place, and matter. But the procession of fire into the paper, aptly represents the presence of divine light to that nature which is capable of its reception. Lastly, the inflammation of the paper may be compared to the deification of mortals, and to the illumination of material natures, which are afterwards carried upwards, like the enkindled paper, from a certain participation of divine seed.

Again, the lotus before the rising of the sun, folds its leaves into itself, but gradually expands them on its rising: unfolding them in proportion to the sun's ascent to the zenith; but as gradually contracting them as that luminary descends to the west. Hence this plant by the expansion and contraction of its leaves appears no less to honour the sun than men by the gesture of their eye-lids, and the motion of their lips. But this imitation and certain participation of supernal light is not only visible in plants, which possess but a vestige of life, but likewise in particular stones. Thus the sun-stone, by its golden rays, imitates those of the sun; but the stone called the eye of heaven, or of the sun, has a figure similar to the pupil of an eye, and a ray shines from the middle of the pupil. Thus too the lunar stone, which has a figure similar to the moon when horned, by a certain change of itself, follows the lunar motion. Lastly, the stone called Helioselenus, i. e. of the sun and moon, imitates after a manner the congress of those luminaries, which it images by its colour. So that all things are full of divine natures; terrestrial natures receiving the plenitude of such as are celestial, but celestial of supercelestial essences; while every order of things proceeds gradually in a beautiful descent, from the highest to the lowest. For whatever is collected into one above the order of things, is afterwards dilated in descending, various souls being distributed under their various ruling divinities.

In the next place, there are many solar animals, such as lions and cocks, which participate, according to their nature, of a certain solar divinity; when it is wonderful how much inferiors yield to superiors in the same order, through they do not yield on magnitude and power. Hence it is said, that a cock is very much feared, and, as it were, reverenced, by a lion; the reason of which we cannot assign from matter or sense, but from  the contemplation alone of a supernal order. For thus we shall fine that the presence of the solar virtue accords more with a cock than with a lion. This will be evident from considering that the cock, as it were with certain hymns, applauds and calls to the rising sun, when he bends his course to us from the antipodes; and that the solar angels sometimes appear in forms of this kind, who, though they are without shape, yet present themselves to us, who are connected with shape, in some sensible form. Sometimes too, there are dæmons with a leonine front, who when a cock is placed before them, unless they are of a solar order, suddenly disappear; and this because those natures which have an inferior rank in the same order always reverence their superiors; just as many, on beholding the images of divine men, are accustomed, from the very view, to be fearful of perpetrating any thing base.

In fine, some things turn round correspondent to the revolutions of the sun, and others after a manner imitate the solar rays, as the palm and the date: some the fiery nature of the sun as the laurel, and other a different property. For indeed we may perceive the properties which are collected in the sun, every where distributed to subsequent natures constituted in a solar order; that is, to angels, dæmons, souls, animals, plants, and stones. Hence the authors of the ancient priesthood, discovered from things apparent, the worship of superior powers, while they mingled some things, and purified with others. They mingled many things indeed together, because they saw that some simple substances possessed a divine property (though not taken singly) sufficient to call down that particular power, of which they were participants. Hence by the mingling of many things together, they attracted upon us a supernal influx; and by the composition of one thing from many, they symbolised with that one, which is above many; and composed statues from the mixtures of various substances, conspiring in sympathy and consent. Besides this, they collected composite odours, by a divine art, into one, comprehending a multitude of powers, and symbolizing, with the unity of a divine essence; considering  that division debilitates each of these, but that mingling them together restores them to the idea of their exemplar.

But sometimes one herb, or one stone, is sufficient to a divine operation. Thus a thistle is sufficient to procure the sudden appearance of some superior power; but laurel, raccinum (or a thorny kind of sprig), the land and sea onion, the coral, the diamond, and the jasper, operate as a safeguard. The heart of a mole is subservient to divination, but sulphur and marine water to purification. Hence the ancient priests, by the mutual relation and sympathy of things to one another, collected their virtues into one, but expelled them by repugnancy and antipathy; purifying, when it was requisite, with sulphur and bitumen, and the sprinkling of marine water. For sulphur purifies from the sharpness of its odour; but marine water on account of its fiery portion. Besides this, in the worship of the Gods, they offered animals, and other substances congruous to their nature; and received in the first place the powers of dæmons as proximate to natural substances and operations, by whose assistance they evocated these natural bodies to which the they approached into their presence. Afterwards they proceeded from dæmons to the powers and energies of the Gods, partly indeed from dæmoniacal instruction, but partly by their own industry, aptly interpreting symbols, and ascending to a proper intelligence of the Gods. And lastly laying aside natural substances and their operations, they received themselves into the communion and fellowship of the Gods.

Taken from On the Mysteries, Iamblichus,  tr Thomas Taylor, p. 343 to 347, 1895 edition.