Bernard Gui, Vita S. Thomae Aquinatis 15 (=Fontes Vitae S. Thomae Aquinatis, ed. D. Prümmer, vol. 3, pp. 161-263), trans. Kenelm Foster, O.P. (The life of Saint Thomas Aquinas: biographical documents, trans. and ed. Kenelm Foster, O.P. (London: Longmans, Green and Co; Baltimore: Helicon Press, 1959), 37). This theme is continued in secs. 16 (mission of Sts. Peter and Paul) and 24 (Jesus himself), as elsewhere. Cf. chap. 30 of William of Tocco's Ystoria sancti Thome de Aquino:
like Solomon [he] asked for nothing from God but wisdom. Hence it may easily be believed, nay the fact is manifest, that it was through the merits of his prayer and piety that he received what he taught and wrote and dictated. This we have, too, from the mouth of brother Reginald, his socius, who was in his master's confidence and saw things that he did not reveal while the latter was still living. But after the death of his master, when Reginald returned to Naples from Fossanova, and resumed his lecturing (for he was a lector) he spoke thus, with many tears: 'My brothers, while my master lived he would not let me reveal the wonderful things I knew about him, among which was this, that his amazing knowledge was not an effect of human intelligence but of prayer. For always, before he studied or disputed or lectured or wrote or dictated, he would pray from the heart, begging with tears to be shown the truth about the divine things that he had to investigate. . . . And when any difficulty arose he . . . had recourse to prayer, whereupon the matter would become wonderfully clear to him. Thus, in his soul, intellect and desire somehow contained each other, the two faculties freely serving one another in such a way that each in turn took the lead: his desire, through prayer, gained access to divine realities, which then the intellect, deeply apprehending, drew into a light which kindled to greater intensity the flame of love'(70n44). Cf. Ystoria sancti Thome de Aquino de Guillaume de Tocco (1323) (=Fontes Vitae S. Thomae Aquinatis, ed. D. Prümmer, vol. 2, pp. 59-160), ed. Claire le Brun-Gouanvic, Studies and texts 127 (Toronto: Pontifical Institute of Medieval Studies, 1996), 157-158, and in a French translation, L'histoire de saint Thomas d'Aquin, trans. Claire le Brun-Gouanvic, Sagesses chrétiennes (Paris: Cerf, 2005), 80-81. In German: Das Leben des heiligen Thomas von Aquino erzählt von Wilhelm von Tocco und andere Zeugnisse zu seinem Leben, trans. Willehad Paul Eckert, Heilige der ungeteilten Christenheit dargstellt von den Zeugen ihres Lebens, ed. Walter Nigg and Wilhelm Schamoni (Düsseldorf: Patmos-Verlag, 1965), 125-126.
Yet there was, of course, a vast ocean of insight yet to come, there being limits to what "'can be answered, in human language, by man still living in this mortal life'":
'Reginald, my son, I will tell you a secret which you must not repeat to anyone while I remain alive. All my writing is now at an end; for such things have been revealed to me that all I have taught and written seems quite trivial to me now. The only thing I want now is that as God has put an end to my writing, He may quickly end my life also'(Bernard Gui, Vita 27, trans. Foster (p. 46)). Cf. chap. 47 of the Life by Tocco, chap. 24 of the Life by Calo, and most famously chap. 79 of the first inquiry into canonization (or Bartholomew of Capua), which appears on pp. 109-110 of this translation by Foster ("'all that I have written seems to me so much straw'"; "'All that I have written seems to me like straw compared with what has now been revealed to me'"). And
'You have written well, Thomas, of the sacrament of my Body; you have answered the question put to you as well as it can be answered, in human language, by man still living in this mortal life.'(Bernard Gui, Vita 24, trans. Foster (p. 44), italics mine).
Moreover, this was as far from a tradition- or church-deprecating illuminism as it could have been. For on this same deathbed St. Thomas is also supposed to have said, addressing Christ himself in the viaticum,
O price of my redemption and food for my pilgrimage, I receive You. For Your sake I have studied and toiled and kept vigil. I have preached You and taught You. Never consciously have I said a word against You. But if I should have said or written anything amiss on this sacrament or any of the others, I leave it all to the judgment of the holy Roman Church, in obedience to whom I desire to end my life(Bernard Gui, Vita 39, trans. Foster (pp. 55-56)).
See also this note here.