B. Against the Opinion of Abbott Joachim

10. This second thing in the opinion of Joachim is heretical, namely that Father and Son and Holy Spirit are not some one thing, because as is argued in the afore cited chapter [of the Decretals, n.8], ‘The Father by generating gave his essence to the Son’ (for he could give nothing else by which the Son would be God), and for a like reason both gave their essence to the Holy Spirit; ‘for the communication was not of part of the essence, because the essence is simple and indivisible, - therefore of the whole essence; therefore the whole same essence, which is in the Father, is in the Son and in the Holy Spirit, and, because of the divine simplicity, each person is that thing, and all three persons are that thing’.

11. Now as to what Joachim argued from the Gospel [n.9], it is there solved, for ‘the Savior understands in his prayer that his faithful are one in a unity proportional to themselves, just as the Father and Son are one in a unity proportional to themselves, -that is, just as the Father and Son are one in the unity of charity which is their nature, so the faithful are one in participated charity’. And this exposition is there proved by the like saying of the Savior (Matthew 5.48) saying to his disciples: “Be ye perfect even as your heavenly Father is perfect,” namely with essential goodness; where he did not admonish that we be perfect of ourselves naturally, as the heavenly Father is perfect of himself naturally, with a perfection essentially belonging to himself, but that we be perfect with the perfection belonging to us, namely of grace and the virtues.