Prooemium Sancti Bonaventurae In Librum Primum Sententiarum 
“He has searched the depths of rivers, and has brought forth into light hidden things” [profunda fluviorum scrutatus est, et abscondita produxit in lucem].Job XXVII, 11
That word, which has been accepted from Job twenty-eight, having been considered more diligently by us uncovers the way for foreknowing [ad praecognoscendum] the fourfold genus of cause in the book of Sentences, namely the material, the formal, the efficient, and the final. For in fact the material cause is intimated in the name “of the rivers” [fluviorum], the formal cause in the searching of the “depths” [profundorum], the final cause in the revelation of “hidden things” [absconditorum], the efficient cause truly is understood in the positing of two words, namely “he has searched” [scrutatus est] and “has brought forth into light” [produxit in lucem].
The material cause is intimated in the name fluviorum in many ways, not in one, so that not only is grasped the matter or subject of the whole book in general, but also of particular books specifically [in speciali]. On account of this it should be noted, that adjoining the fourfold property of a material river there is a fourfold spiritual river, about which, according to a fourfold difference, are the four books of the Sentences. For in fact I consider a material river, how far [its] duration [quoad durationem], and I find perpetuity. For as Isidore says: “A river is perennial.” I consider how great [it is] according to [its] extension [quantum ad extensionem], and I find spaciousness. For in this a river is distinguished from a stream. I consider how great [it is] according to [its] motion [quantum ad motum], and I find circularity. For as is said in the first [chapter] of Ecclesiastes: “To the place from which rivers flow forth, they are returned . . .” I consider the effect [of a material river], and I find cleansing. For a river, on account of the abundance of [its] waters, cleanses the lands through which it flows, [but] such that it is not stained. And because all things transferring [transferentes] transfer according to some likeness, from this fourfold metaphor having been accepted conditionally, a fourfold river in spiritual [things] is found, as we are able to collect from the Scriptures.
First, on account of perpetuity the emanation of persons is called a river, because that emanation alone is without beginning, without end. About this river [it is written in] Daniel seven: “The ancient of days sat, and a river fiery and rapid was going out from his face.” That ancient of days is the eternal Father, the antiquity of whom is eternity. That ancient one sat, since not only in him is eternity, but also immutability. From the face of the ancient one was going out a river fiery and rapid, that is, from the sublimity of his divinity was proceeding a plenitude of love and a plenitude of strength [virtutis]: a plenitude of strength in the Son, therefore the river was rapid; a plenitude of love in the Holy Spirit, and therefore the river was fiery.
Second, on account of spaciousness the production of worldly [mundanarum] things is called a river, for which cause [it is called] not only a river, but that world is called the sea by the Prophet in the Psalm: This sea great and spacious etc. About this river Ezekiel [wrote] in the twenty-ninth [chapter]: “Behold I [am] against thee, Pharaoh, king of Egypt, great dragon, who lie in the middle of rivers and say: ‘The river is mine, and I made my own self.’ And I will put a bridle in your jaws” etc. That great dragon, whom the Lord addresses and whom he threatens in the figure and person of Pharaoh, is the devil, who is the king of Egypt, because he reigns over them, whom he has blinded [excaecavit] in the darkness of error, as think are the heretics, to whom indeed he says: “The river is mine, and I made my own self,” as if he himself made the very world [mundum istum] and himself does not have another source [principium]. This error he himself spoke and suggested to the impious Manichaeans, who contend that the whole machine of visible things [machinam visibilium] has been built [conditam] by an evil God. The jaws of this dragon the Lord will bridle, when, with the power for him of suggesting falsehoods having been born away [ablata sibi potestate suggerendi falsa], he will show that he himself is the builder [conditorem] of this river; hence in the same authority it follows: All the inhabitants of Egypt shall know, that I [am] the Lord.
Third, on account of circularity the Incarnation of the Son of God is called a river, because, as in a circle the end [ultimum] is conjoined with the beginning [principio], thus in the Incarnation the highest [supremum] is conjoined with the lowest [imo], as God [is conjoined] with mud, and the first with the last, as the eternal Son of God with man constructed on the sixth day. About this river [it is written] in the twenty-fourth [chapter] of Ecclesiasticus: I, as if the river Dorix, and as an aqueduct came forth from paradise. “Dorix” is interpreted the medicine of generation, and is there figurative speech [figurativus sermo], so that it is understood conversely, that is, [as] the generation of medicine. For the Incarnation of the Son of God was nothing other than the generation of medicine: For truly our weaknesses he himself bore and our infirmities he himself carried. Rightly therefore the Incarnation of the Son is called the river Dorix. And Christ himself says truly about himself: I, as if the river Dorix, that is, the medicinal river, and as an aqueduct came forth from paradise. This is the nature of water, that as much as it ascends, so much it descends. Such was the coming forth [exitus] of the Incarnation, according as it is said in the Psalm: From the highest heaven its going out [egressio], and its running [occursus] up to its highest. And in the sixteenth [chapter] of John: I have come forth from the Father and I have come into the world: again I leave behind the world and I go to the Father, and thus he made a circle. About this river also, with respect to its going out [quantum ad egressum] from its mother, that is able to be explained, which is said in the tenth [chapter] of Esther in the dream of Mardochaeus: A small stream arises into a river, and is converted into light and the sun. Who, I entreat, is that small stream if not the most humble Virgin? This arose into a river, when she brought forth [generavit] Christ, who is called not only a river through abundance of grace, but also light of wisdom and sun of justice, according as John speaks of him in the first chapter: He was the true light etc.
Fourth, on account of cleansing the dispensation of Sacraments is called a river, which without pollution of itself cleanses us from the defilements of sins. About this river [it is written] in the twenty-second [chapter] of the Apocalypse: He showed to me a river of the water of life, splendid as crystal, proceeding from the seat of God and of the Lamb. The dispensation of Sacraments is called a river “splendid as crystal” on account of clarity and brightness, which it bequeaths in souls, which are purified in this river. It is also called a river “of the water of life” on account of the efficacy of grace, which vivifies the soul. This also proceeds “from the seat of God and of the Lamb.” For sacramental grace proceeds from God as from author and efficient [cause], from Christ as from mediator and from meriting [cause] [promerente]. On account of which all Sacraments are said to have efficacy from the passion of Christ; hence Augustine testifies: “From the side of Christ sleeping [on the cross] flowed the Sacraments, when thence flowed blood and water.”
. Latin text used: Opera Omnia, Edita Studio et cura pp. Collegii a S. Bonaventura. Accessed online: https://catalog.hathitrust.org/Record/011922185