16. Passing by, then, these reasoners, who are unable to know the substance even of the soul, which is invisible, and therefore are very far indeed from knowing that the substance of the one and only God, that is, the Father and the Son and the Holy Spirit, remains ever not only invisible, but also unchangeable, and that hence it possesses true and real immortality; let us, who deny that God, whether the Father, or the Son, or the Holy Spirit, ever appeared to bodily eyes, unless through the corporeal creature made subject to His own power; let us, I say—ready to be corrected, if we are reproved in a fraternal and upright spirit, ready to be so, even if carped at by an enemy, so that he speak the truth—in catholic peace and with peaceful study inquire, whether God indiscriminately appeared to our fathers before Christ came in the flesh, or whether it was any one person of the Trinity, or whether severally, as it were by turns.