J. I. Packer on meditation:

Meditation is the activity of calling to mind, thinking over, dwelling on, and applying to oneself the various things one knows about the works and ways and purpose 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 communication 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.