[…] This prayer is commended in the Gospels; it is set forth as an example of prayer, and it becomes our sacred duty to piously contemplate it.
Why didn’t the publican choose some majestic and moving psalm by which to pour out his heart before God, but instead had recourse to such a brief prayer?
[…] When true repentance begins to shudder in the soul, when humility and contrition of spirit arises there because one’s eyes have been opened to the soul’s sinfulness, then loquacity becomes unbearable, impossible.
Concentrating within itself, turning all its attention upon its disastrous condition, the soul begins to call out to God through some form of short, concise prayer.
When an encompassing view of his own sinfulness is granted to a person by God, it cannot be described by eloquent speech or an abundance of words.
More exactly, the person expresses this awareness by sighs and groaning of soul, clothed in very brief and simple words.
Whoever wishes to unfold a deep feeling of repentance within himself uses short prayer to reach that state, pronounced with as much attention and reverence as possible.
Abandoning excessive words, even though they be sacred words, allows the mind to completely free itself of distractions and to strive for introspection with all its strength.
“When you pray, do not permit yourself to use many words,” says St. John Climacus, “so that your mind might not be distracted from considering the words.
“One word from the publican brought him God’s mercy, and one faithful utterance saved the thief. Much speaking in prayer often brings the mind to distraction and dreaminess, while sparse words usually gather the thoughts.”
Because of the great benefit that brief, attentive, concentrated prayer brings, the Holy Church enjoins its children to timely learn some form of brief prayer.
One who has learned such a prayer possesses a ready ability to pray in any place, at any time. While traveling, in the refectory, doing handiwork, or in the company of others, he can cry out to God.
When it is not possible to pray with the lips, it is possible to pray with the mind.
The convenience of brief prayer is obvious in this regard: it is quite easy to lose the meaning and order of lengthy prayers when we are occupied with something else, while short prayer always preserves its integrity.
If it is left off for a time, one can return to it with little difficulty.
Ignatius Brianchaninov (1807–1867; Russian Orthodox): Homily on the Sunday of the Publican and the Pharisee on Prayer and Repentance translated by Nun Cornelia Rees @ Pravoslavie.