St. Augustine sheds helpful light on how we pray without ceasing…
“And all my desire is before you” (Ps 37:10)… This very desire of yours is your prayer; and if your desire is continual, your prayer is continual too. It was not for nothing that the Apostle said: “Pray without ceasing” (1Thes 5,17). Can we unceasingly bend our knees, bow down our bodies or uplift our hands, that he should tell us: Pray without ceasing? No; if it is thus he bids up pray, I do not think we can do so without ceasing.
But there is another way of praying, interior and unbroken, and that is the way of desire. Whatever else you are doing, if you long for that sabbath, you are not ceasing to pray. If you do not want to cease praying, do not cease longing.
Your unceasing desire is your unceasing prayer. You will lapse into silence if you lose your longing. Who did lapse into silence? Those of whom it has been said: “Because iniquity hath abounded, the charity of many shall grow cold” (Mt 24.12). The coldness of charity is the heart’s silence; its glowing ardor, the heart’s outcry. If charity is always present, you are ever crying out; if always crying out, you are ever longing; if longing, you have not forgotten the everlasting repose.” (Discourse on Psalm 37)