5 When then are we jubilant? When we praise that which cannot be uttered. For we observe the whole creation, the earth and the sea, and all things that therein are: we observe that each have their sources and causes, the power of production, the order of birth, the limit of duration, the end in decease, that successive ages run on without any confusion, that the stars roll, as it seems, from the East to the West, and complete the courses of the years: we see how the months are measured, how the hours extend; and in all these things a certain invisible element, I know not what, but some principle of unity, which is termed spirit or soul, present in all living things, urging them to the pursuit of pleasure and the avoidance of pain, and the preservation of their own safety; that man also has somewhat in common with the Angels of God; not with cattle, such as life, hearing, sight, and so forth; but somewhat which can understand God, which peculiarly does belong to the mind, which can distinguish justice and injustice, as the eye discerns white from black.
In all this consideration of creation, which I have run over as I could, let the soul ask itself: Who created all these things? Who made them? Who made among them yourself?...I have observed the whole creation, as far as I could. I have observed the bodily creation in heaven and on earth, and the spiritual in myself who am speaking, who animate my limbs, who exert voice, who move the tongue, who pronounce words, and distinguish sensations. And when can I comprehend myself in myself?
How then can I comprehend what is above myself? Yet the sight of God is promised to the human heart, and a certain operation of purifying the heart is enjoined; this is the counsel of Scripture. Provide the means of seeing what you love, before thou try to see it. For unto whom is it not sweet to hear of God and His Name, except to the ungodly, who is far removed, separated from Him?...
Source: The Enarrations, or Expositions, on the Psalms (New Advent)