Above all else, guard your heart,
for everything you do flows from it.
Perhaps the most common mistake the average Christian makes is overestimating his ability to throw off worldly influences that he places before his senses, and that eventually seep into his thinking. Really, if we are honest, these impure thoughts are already in our hearts – “We are tempted by our own desires that drag us off and trap us” (James 1:14) – and we will either feed the thoughts of God or the thoughts of the flesh, of the world, and of the evil one. Feeding the thoughts of God means daily coming to Him in prayer and devotion, daily reading and meditating on His Word, contemplating the writings of Christian authors, confessing sins, receiving the filling of the Spirit.
I have lately come to know a few Christians who disagree with this, who decry the thoughts of having daily devotionals as mere legalism, insisting that they are free from those types of rules. But consider the daily influences of the world that we let into our minds – some of which we have little choice, such as the foul language of co-workers or the advertisements of the world that often cross the barrier of a Christian’s conscience. We need to counteract this daily, and not encourage it, by shutting out of our minds those impure thoughts we can control, and letting in, locking in, the thoughts of God. The problem is more often the simple combination of lust and pride: our lusts that want to see and think about what we should not, and our blinding pride that says we can get away with it without an effect on our souls.
This principle is impossible to ignore and remain growing in our devotion, pure in our thoughts, and fruitful in our service. James Allen wrote in his essay, “As a Man Thinketh.”
Mind is the Master power that moulds and makes,
And Man is Mind, and evermore he takes
The tool of Thought, and, shaping what he wills,
Brings forth a thousand joys, a thousand ills: —
He thinks in secret, and it comes to pass:
Environment is but his looking-glass.
We think “in secret,” imagining that these are private affairs, and to the degree that prying into someone’s private life is inappropriate, that is true, but thoughts that take root in our minds do not remain only in our minds – they “come to pass,” that is, we act them out. Someway our thoughts, especially our secret thoughts, will determine our actions. Then, if we would have productive lives, if we would walk in joy, in peace, and in love, we should focus our thoughts, especially our secret thoughts, on God.
Your eyes are the lamp for your body. When your eyes are good, you have all the light you need. But when your eyes are bad, everything is dark. So be sure that your light isn’t darkness. If you have light, and nothing is dark, then light will be everywhere, as when a lamp shines brightly on you.
We cannot walk down a path without fixing our eyes on the path. If our eyes dart back and forth, if we look up in the sky, or around behind us, or far off the path, we will in variably stumble. We need the light of the truth of God to illuminate our path, “Thy word is a lamp unto my feet…” (Psalm 119:105).
Guard your thoughts. Treasure your mind as the great asset it is. Lock out impurities. Lock in the truth.
We live in this world, but we don’t act like its people or fight our battles with the weapons of this world. Instead, we use God’s power that can destroy fortresses. We destroy arguments and every bit of pride that keeps anyone from knowing God. We capture people’s thoughts and make them obey Christ.
2 Corinthians 10:3-5
Lord, destroy our pride and take our thoughts captive. Create in our hearts a hunger and a thirst for Your truth. Guard our thoughts this day and this night. Amen.
 James Allen, As a Man Thinketh, http://jamesallen.wwwhubs.com/think.htm