From a letter to Proba by Saint Augustine
Let us turn our mind to the task of prayer at appointed hours
Let us always desire the happy life from the Lord God and always pray for it. But for this very reason we turn our mind to the task of prayer at appointed hours, since that desire grows lukewarm, so to speak, from our involvement in other concerns and occupations. We remind ourselves through the words of prayer to focus our attention on the object of our desire; otherwise, the desire that began to grow lukewarm may grow chill altogether and may be totally extinguished unless it is repeatedly stirred into flame.
Therefore, when the Apostle says: Let your petitions become known before God, this should not be taken in the sense that they are in fact becoming known to God who certainly knew them even before they were made, but that they are becoming known to us before God through submission and not before men through boasting.
Since this is the case, it is not wrong or useless to pray even for a long time when there is the opportunity. I mean when it does not keep us from performing the other good and necessary actions we are obliged to do. But even in these actions, as I have said, we must always pray with that desire. To pray for a longer time is not the same as to pray by multiplying words, as some people suppose. Lengthy talk is one thing, a prayerful disposition which lasts a long time is another. For it is even written in reference to the Lord himself that he spent the night in prayer and that he prayed at great length. Was he not giving us an example by this? In time, he prays when it is appropriate; and in eternity, he hears our prayers with the Father.
The monks in Egypt are said to offer frequent prayers, but these are very short and hurled like swift javelins. Otherwise their watchful attention, a very necessary quality for anyone at prayer, could be dulled and could disappear through protracted delays. They also clearly demonstrate through this practice that a person must not quickly divert such attention if it lasts, just as one must not allow it to be blunted if it cannot last.
Excessive talking should be kept out of prayer but that does not mean that one should not spend much time in prayer so long as fervent attitude continues to accompany his prayer. To talk at length in prayer is to perform a necessary action with an excess of words. To spend much time in prayer is to knock with a persistent and holy fervor at the door of the one whom we beseech. This task is generally accomplished more through sighs than words, more through weeping than speech. He places our tears in his sight, and our sighs are not hidden from him, for he has established all things through his Word and does not seek human words