“Another positive sign of a renewed man is that he meditates in the law of the LORD day and night. ‘As a man thinketh in his heart, so is he.’
Vain thoughts lodge in all ungodly men. But the righteous hate sinful imaginings. What the wicked would be ashamed to act or speak out, the righteous is ashamed to think or desire.
Yet the mind of the righteous is full of activity. He meditates. The power of reflection chiefly distinguishes a man from a brute.
The habit of reflection chiefly distinguishes a wise man from a fool. Pious reflection on God’s word greatly distinguishes a saint from a sinner.
Without meditation grace never thrives, prayer is languid, praise dull, and religious duties unprofitable.
Yet to flesh and blood without divine grace this is an impossible duty.
It is easier to take a journey of a thousand miles than to spend an hour in close, devout, profitable thought on divine things.
Like prayer (Luke 18:7), meditation is to be pursued day and night, not reluctantly, but joyously, not merely in God’s house, or on the Lord’s day, but whenever other duties do not forbid.
Nor does the true child of God slight part of divine truth. He loves it all.
A saint is therefore described by his ‘meditating in the law of God day and night,’ which is the natural and necessary effect of his delight in it.”
–William Plumer, Psalms: A Critical and Expository Commentary with Doctrinal and Practical Remarks (Carlisle, PA: Banner of Truth Trust, originally published in 1867; reprinted 2016), 28.