We therefore consider it Our grave duty to exhort you in a special manner to the practice of daily meditation, a practice recommended to all the clergy also by Canon Law. For just as the desire for priestly perfection is nourished and strengthened by daily meditation, so its neglect is the source of distaste for spiritual things, through which piety is lessened and grows languid, and the impulse towards personal sanctification is not only weakened or ceases altogether, but the entire priestly ministry suffers great harm. It must therefore be stated without reservation that no other means has the unique efficacy of meditation, and that, as a consequence, its daily practice can in no wise be substituted for. (Papal Writings, Menti Nostrae, 23 September 1960).