1. Prayer is divinely commanded. Scripture not only commends but enjoins it (see Mt 7.7–11; 26.41; Lk 18.1; Col 4.2–4; 1 Thes 5.16–18). There is a profound reason for this.
2. Scripture and the Holy Eucharist are paired as two tables of the new law; they are two forms in which the Word of God comes to us (see DV 21, 25, 26; AA 6; AG 6). God’s words and acts together give us himself in personal wholeness. Hence our side of the relationship requires prayer—the conversation with God who speaks to us in Scripture—just as much as it requires reception of the Eucharist. By both of these acts, we accept and assimilate the bread which has come down from heaven.
The general point that prayer is necessary for our side of the relationship of revelation and faith includes all the specific ways in which prayer is required to live the Christian life. Speaking of self-control, for example, Leo XIII explains why faith and prayer are necessary to cultivate this virtue: “The virtue of which we speak, like the others, is produced and nourished by divine faith; for God is the Author of all true blessings that are to be desired for themselves, as we owe to Him our knowledge of His infinite goodness, and our knowledge of the merits of our Redeemer. But, again, nothing is more fitted for the nourishment of divine faith than the pious habit of prayer, and the need of it at this time is seen by its weakness in most, and its absence in many men. For that virtue is especially the source whereby not only private lives may be amended, but also from which a final judgment may be looked for in those matters which in the daily conflict of men do not permit states to live in peace and security. If the multitude is frenzied with a thirst for excessive liberty, if the inhuman lust of the rich never is satisfied, and if to these be added those evils of the same kind to which We have referred fully above, it will be found that nothing can heal them more completely or fully than Christian faith.”4 Pope Leo then goes on to exhort clerics to lead exemplary lives thoroughly formed by prayer, because otherwise their learning, teaching, and preaching cannot be fruitful.
3. Acts of prayer are human acts by which one fulfills and determines oneself. These acts last; they build up one’s Christian personality. As a man and woman become husband and wife more and more perfectly by constant, loving communion, so human persons and the indwelling Trinity become more and more perfectly united by constant prayer.
4. The analogy with the interpersonal relationship of husband and wife sheds further light on the need for prayer. The whole common life of a married couple depends on mutual understanding, which in turn requires conversation. Such conversation cannot always be directed to some practical object. Sometimes they must converse simply to commune, a communing which reaches a peak in the play of love. As marriage requires such communing, Christian life requires prayer (see S.t., 2–2, q. 82, a. 2, ad 2).
Because prayer is a fulfilling human act, it ought not to be engaged in as if it were labor or bitter medicine to be taken in small doses only for the sake of its health-giving effects. Like play, prayer is essentially a leisurely activity, something worth doing for its own sake (see S.t., 2–2, q. 82, a. 4). However, this does not mean prayer should be playful in the sense that one should engage in it only when and as long as one finds it pleasant, nor that one may engage in it in a careless manner. If one ought to be conscientious in labor and take pride in work well done, even when done for some ulterior end, how much more ought one to be conscientious in the best form of leisure activity and seek to do it well.
4. Leo XIII, Exeunte iam anno, 21 ASS (1888) 330; The Papal Encyclicals, 108.13.