The Spirit pleads for us
There is then within us a kind of instructed ignorance, instructed, that is, by the Spirit of God who helps our weakness. When the Apostle said: "If we hope for something we do not see, we look forward to it with patience", he added, "In the same way the Spirit helps our weakness; we do not know what it is right to pray for, but the Spirit himself pleads with sighs too deep for words. He who searches hearts knows what the Spirit means, for he pleads for the saints according to God’s will" (Romans, 8:25-27).
We must not understand by this that the Holy Spirit of God pleads for the saints as if he were someone different from what God is: in the Trinity the Spirit is the unchangeable God and one God with the Father and the Son. Scripture says: He pleads for the saints because he moves the saints to plead, just as it says: "The Lord your God tests you, to know if you love him" (Dt 13, 4), in this sense, that he does it to enable you to know.
(Ep. 130, 14, 27-15, 28: CSEL 44, 71-73)
Peter Paul Rubens. St Augustine. 1639. National Gallery, Prague.