J. I. Packer gives a rich definition of meditation:
Meditation is the activity of calling to mind, and thinking over, and dwelling on, and applying to oneself, the various things that one knows about the works and ways and purposes and promises of God. It is an activity of holy thought, consciously performed in the presence of God, under the eye of God, by the help of God, as a means of communion with God.
Its purpose is to clear one’s mental and spiritual vision of God, and to let his truth make its full and proper impact on one’s mind and heart. It is a matter of talking to oneself about God and oneself; it is, indeed, often a matter of arguing with oneself, reasoning oneself out of moods of doubt and unbelief into a clear apprehension of God’s power and grace.
There is no point in being original for its own sake when the work of another has sufficiently made the point. Mr. Packer seems to have chosen every word with care and spiritual wisdom, though his appreciation of the Puritans certainly contributed to this definition, as is evident from their writings on the topic. So then, it would be simplest to break down the subject as he has broken it down.
“Meditation is the activity of calling to mind, and thinking over, and dwelling on, and applying to oneself, the various things that one knows about the works and ways and purposes and promises of God.” It is thus a disciplined activity. We readily recall the command, “Think on these things,” and indeed, this is the idea of meditation. The word Paul uses in Philippians 4 for “think” is logizomai, and it is the same word for “reckon” and “impute” in Romans 4 regarding justification. What God does in a legal sense toward sinners we are to do in a moral sense toward concepts by meditation. God decidedly beheld the sinner, declared him righteous on the basis of faith, and permanently viewed the individual according to that declaration. So, when we meditate on God, the goal is not simply to think about Him and then leave His presence. We desire to accomplish something. We desire to come away from meditation with an opinion and appreciation and passion for what we have just considered. We have decided to think on it, we have weighed its factors, and we have intelligently made it “ours” by concluding something about it that will forever frame how we view it henceforth. This is the epitome of delighting in God’s Law. We are not only aiming to understand it; we want it to be impressed on our souls. It is a love for quality not quantity.
“It is an activity of holy thought, consciously performed in the presence of God, under the eye of God, by the help of God, as a means of communion with God.” This is the idea when David says, “Let the words of my mouth and the meditation of my heart be acceptable in Your sight, O Lord, my rock and my Redeemer” (Psalm 19:14). He recognized in another psalm (139) that God knew his thoughts before they exited his lips in prayer; therefore, if God knows thoughts, why should the thought life not be consecrated to Him in quiet meditation? As with any relationship, words are not the only means of deepening the mutual affection. Two can appreciate art together and so gravitate toward each other because of mutual taste. So, meditation brings us closer to God’s heart as the Spirit makes us appreciate things in the way He does. Though we are not speaking constantly to Him, we are aware that He is with us and so commune with Him by sharing His thoughts through His word.
“Its purpose is to clear one’s mental and spiritual vision of God, and to let his truth make its full and proper impact on one’s mind and heart.” To study the Bible is necessary, but even reprobates study the Bible for the sake of religion or academics. What capacity distinguishes the Christian from men such as these? The ability to receive Scripture in the heart. Scripture is meant to crush pride, encourage the weak, change the will, empower the life, and stir up worship. The power of Scripture comes not through study alone (though it is necessary), but it comes by deliberate thought and self-examination. It is not good enough to study Scripture: do you receive Scripture in all its fullness? Do you love it? Are you challenged by it? Does it give you lasting strength and encouragement? Does it modify your will?
“It is a matter of talking to oneself about God and oneself; it is, indeed, often a matter of arguing with oneself, reasoning oneself out of moods of doubt and unbelief into a clear apprehension of God’s power and grace.” The Hebrew word for “meditation” connotes groaning and sighing as well as contemplating. The imagery is a man whose mind is unsettled as he tries to close the gaps in his thinking by pondering long the subject of present emotional impact. Psalm 77 is a perfect example of this, and we will look at this later. Meditation is a powerful thing. Its aim is to subdue the flesh. The flesh causes us to fear, but meditation fights back and says, “No, consider the faithfulness of God. Consider His faithfulness to Abraham, Job, Daniel. What good reason do you have to believe He will not be faithful to you?” The flesh responds, “But my circumstance seems impossible.” Meditation responds, “No, you must believe, for ‘I can do all things through Christ.’” The flesh tries to cower, but meditation keeps beating it with promises and so struggles into determined faith in God. As a result, the Christian has learned to translate words into reality and thus has learned the power of God. It gets to the end of the thing, whether it be sinful stubbornness or sad discouragement. It determines to view God in a way that He becomes our greatest resource. It cannot leave until what it knows of Scripture becomes what it depends on entirely. We are truly “bringing every thought captive to the obedience of Christ.”
 Knowing God by J. I. Packer (Downers Grove, IL: InterVarsity Press, 1993), p. 23.