REGULA 1–3: one essence; common to three persons; attributes one in essence
RULE. 1. God is so one that He is unique, and does not have many essences. The reason of the former is that it cannot happen that there be several first or highest and infinite principles. The reason of the latter is that God through one and the same essence is immutable, eternal, wise, good, omnipotent. Therefore God does not have many essences diverse or opposed, extreme or moderate, real or accidental, general and specific partial: but an essence so one in number or individual that it does not admit a principle of individuation.
2. The essence of God is common to the three persons: yet it is not one in genus or species. For it is not multiplied in the persons as a universal thing: but equally is in each as an infinite singular thing. 3. The multitude of God's attributes does not fight with the unity of God's essence; because all those attributes are one in essence. For they are nothing other than one and the same essence of God related to various objects and effects. So God's eternity is God's very essence insofar as it has no beginning, succession, and end of duration. God's omnipotence is God's very essence insofar as it can effect every good.
Latin
REGULA. 1. Deus ita est unus, ut sit unicus, nec habeat multas essentias. Ratio prioris est, quia fieri non potest, ut plura sint prima sive summa & infinita principia. Ratio posterioris est, quia Deus per unam eandemque essentiam est immutabilis, aeternus, sapiens, bonus, omnipotens. Quapropter Deus non habet multas essentias diversas vel adversas, intensas vel remissas, substantiales vel accidentales, genericas & specificam, totales vel partiales: sed essentiam ita unam numero seu individuam, ut non admittat principium individuationis. 2. Essentia Dei est communis tribus personis: non tamen est una genere vel specie. Neque enim multiplicatur in personis, ut res universalis: sed aequaliter est in singulis ut res singularis infinita. 3. Multitudo attributorum Dei non pugnat cum unitate essentiae Dei; quia omnia ista attributa sunt unum in essentia. Nihil enim sunt aliud, quam una eademque Dei essentia relata ad varia objecta & effecta. Sic aeternitas Dei est ipsa Dei essentia, quatenus non habet initium, successionem & finem durationis. Omnipotentia Dei est ipsa Dei essentia, quatenus efficere potest omne bonum.