Transformation in the life of the believer begins with a renewal of the mind (Rom. 12:1-2; Eph. 4:22-24). So what kinds of things should be the focus of the believer’s meditation so that his mind is daily transformed to the image of Christ? Stephen Charnock provides some answers [I've formatted this in a block paragraph style to indicate the flow of his thought. The original text had this as one single paragraph. The wording remains unchanged.]:
Let it be some truth which will assist you in reviving some languishing grace, or fortify you against some triumphing corruption; for it is our darling sin which doth most envenom our thoughts: Prov. xxiii. 7, ‘As a man thinks in his heart, so is he.’
As if you have a thirst for honour, let your fancy represent the honour of being a child of God and heir of heaven.
If you are inclined to covetousness, think of the riches stored up in a Saviour, and dispensed by him;
if to voluptuousness, fancy the pleasures in the ways of wisdom here, and at God’s right hand hereafter.
This is to deal with our hearts as Paul with his hearers, to catch them with guile.
Stake your soul down to some serious and profitable mystery of religion;
as the majesty of God, some particular attribute,
his condescension in Christ,
the love of our Redeemer,
the value of his suff’erings,
the virtue of his blood,
the end of his ascension,
the work of the Spirit,
the excellency of the soul,
beauty of holiness,
certainty of death,
terror of judgments,
torments of hell,
and joys of heaven.
Why may not that which was the subject of God’s innumerable thoughts, Ps. xl. 5, be the subject of ours?
God’s thoughts and counsels were concerning Christ,
the end of his coming,
his precepts of holiness,
and promises of life;
and that not only speculatively, but with an infinite pleasure in his own glory, and the creatures’ good to be accomplished by him.
Would it not be work enough for our thoughts all the day, to travel over the length, breadth, height, and depth of the love of Christ?
Would the greatness of the journey give us leisure to make any starts out of the way?
Having settled the theme for all the day, we shall find occasional assistances, even from worldly businesses; as scholars, who have some exercises to make, find helps in their own course of reading, though the book hath no designed respect to their proper theme.
Thus, by employing our minds about one thing chiefly, we shall not only hinder them from vain excursions, but make even common objects to be oil to our good thoughts, which otherwise would have been fuel for our bad.
Such generous liquor would scent our minds and conversations all the day,
that whatsoever motions came into our hearts would be tinctured with this spirit
and savour of our morning thoughts;
as vessels, having been filled with a rich wine, communicate a relish of it to the liquors afterwards put into them.
We might also more steadily go about our worldly business if we carry God in our minds; as one foot of the compass will more regularly move about the circumference when the other remains firm in the centre. [The Works of Stephen Charnock, V: 307-8.]