In this passage, Teresa discusses the soul’s certainty after it has experienced the “Prayer of Union.” In Interior Castle, Teresa uses various terms to roughly describe deepening experiences of passive prayer – sometimes referred to as contemplation or infused contemplation in the Catholic Tradition. Up to this point in the work her progression has been Prayer of Recollection > Prayer of Quiet (also called “Consolations”) > Prayer of Union. Catholic mystics of this period do not seem to be systematic about their descriptions in this regard, and terminology can sometimes be interchangeable or hazy. It may be helpful to think of these authors as grasping for language to describe their experience, which they often claim is ineffable or indescribable.
“Turning now to the indication which I have described as a decisive one: here is a soul which God has made, as it were, completely foolish in order the better to impress upon it true wisdom. For as long as a soul is in this state, it can neither see nor hear nor understand: the period is always short and seems to the soul shorter than it really is. God implants Himself in the interior of that soul is such a way that, when it returns to itself, it cannot possibly doubt that God has been in it and it has been in God; so firmly does this truth remain within it that, although for years God may never grant it that favour again, it can neither forget it nor doubt that it has received it (and this quite apart from the effects which remain within it, and of which I will speak later). The certainty of the soul is very material.
But now you will say to me: How did the soul see it and understand it if it can neither see nor understand? I am not saying that it saw it at the time, but that it sees it clearly afterwards, and not because if it is a vision (sic), but because of a certainty which remains in the soul, which can be put there only by God…
How, you will ask, can we become so convinced of what we have not seen? That I do not know; it is the work of God. But I know I am speaking the truth; and if anyone has not that certainty, I should say that what he has experienced is not union of the whole soul with God…”