Saint Alphonsus Liguori, Doctor of Moral Theology and called by the Popes the Prince of all Moral Theologians, has written very extensively on the importance and practice of meditation; which he calls mental prayer. More than writing about mental prayer, he practiced it daily and climbed up to great heights of holiness and perfection.
In his great work, 'The Way of Salvation and Perfection', here is what he says about daily meditation:
"Take care to make half an hour’s meditation as soon as possible in the day. For though meditation is not absolutely necessary, it is morally necessary, in order to obtain the grace of perseverance. Those who neglect it will find it very difficult to persevere in the grace of God. Now, prayer is necessary, not merely as a precept, but as a means to observe the Commandments, since, as a general rule, and speaking of adults, God only gives his grace to those who ask for it. But without meditation, a person has a very faint notion of his own spiritual wants, and he is moreover but slightly impressed with the necessity of praying, in order to overcome temptations and to save his soul: thus he is led to pray but little or nothing, and for want of prayer is eventually lost."
I suppose most of us say our daily vocal prayers: the morning offering, night prayers, grace before and after meals, the Rosary and other devotions we might have. Do you, however, meditate on the Life and Mysteries of Our Lord in silence daily? Again, this meditation has to be silent and the Holy Bible and other books of piety may be used to kindle in us holy affections of love for God. Do you make for time for this meditation which, as St. Alphonsus shows, is necessary for salvation? Examine yourself, confess, and resolve to daily join in this mystical conversation between your soul and God.