— when our desire shall be satisfied with good things, and when there shall be nothing beyond to be sought after with groaning, but all things shall be possessed by us with rejoicing.
At the same time, because this blessing is nothing else than the “peace which passeth all understanding,” even when we are asking it in our prayers, we know not what to pray for as we ought.
For inasmuch as we cannot present it to our minds as it really is, we do not know it, but whatever image of it may be presented to our minds we reject, disown, and condemn;
we know it is not what we are seeking, although we do not yet know enough to be able to define what we seek.
There is therefore in us a certain learned ignorance, so to speak — an ignorance which we learn from that Spirit of God who helps our infirmities.
For after the apostle said, “If we hope for that we see not, then do we with patience wait for it,” he added in the same passage:
“Likewise the Spirit also helpeth our infirmities: for we know not what we should pray for as we ought, but the Spirit itself maketh intercession for us, with groanings which cannot be uttered. And He that searcheth the hearts knoweth what is in the mind of the Spirit, because He maketh intercession for the saints according to the will of God.”
This is not to be understood as if it meant that the Holy Spirit of God, who is in the Trinity, God unchangeable, and is one God with the Father and the Son, intercedes for the saints like one who is not a divine person;
for it is said, “He maketh intercession for the saints,” because He enables the saints to make intercession, as in another place it is said, “The Lord your God proves you, that He may know whether ye love Him,” i.e. that He may make you know.
He therefore makes the saints intercede with groanings which cannot be uttered, when He inspires them with longings for that great blessing, as yet unknown, for which we patiently wait.
For how is that which is desired set forth in language if it be unknown, for if it were utterly unknown it would not be desired; and on the other hand, if it were seen, it would not be desired nor sought for with groanings?
Augustine of Hippo (354-430): Letter to Proba, XIV, 27; XV, 28 @ Crossroads Initiative.