3 But being placed under pressure, we are crushed for this purpose, that for our love by which we were borne towards those worldly, secular, temporal, unstable, and perishable things, having suffered in them, in this life, torments, and tribulations of pressures, and abundance of temptations, we may begin to seek that rest which is not of this life, nor of this earth; and the Lord becomes, as is written, “a refuge for the poor man.” What is, “for the poor man”? For him who is, as it were, destitute, without aid, without help, without anything on which he may rest, in earth.
For to such poor men, God is present. For though men abound in money on earth,...they are filled more with fear than with enjoyment. For what is so uncertain as a rolling thing? It is not unfitly that money itself is stamped round, because it remains not still. Such men, therefore, though they have something, are yet poor. But those who have none of this wealth, but only desire it, are counted also among rich men who will be rejected; for God takes account not of power, but of will.
The poor then are destitute of all this world's substance, for even though it abounds around them, they know how fleeting it is; and crying unto God, having nothing in this world with which they may delight themselves, and be held down, placed in abundant pressures and temptations, as if in winepresses, they flow down, having become oil or wine. What are these latter but good desires? For God remains their only object of desire; now they love not earth. For they love Him who made heaven and earth; they love Him, and are not yet with Him.
Their desire is delayed, in order that it may increase; it increases, in order that it may receive. For it is not any little thing that God will give to him who desires, nor does he need to be little exercised to be made fit to receive so great a good: not anything which He has made will God give, but Himself who made all things. Exercise yourself to receive God: that which you shall have for ever, desire thou for a long time....
Source: The Enarrations, or Expositions, on the Psalms (New Advent)