From Imitation of Christ by Thomas á Kempis:

The Voice of Christ
My child, you should give all for all, and in no way belong to yourself. You must know that self-love is more harmful to you than anything else in the world. In proportion to the love and affection you have for a thing, it will cling to you more or less. If your love is pure, simple, and well ordered [like the Child in the manger], you will not be a slave to anything. Do not covet what you may not have. Do not possess anything that can hinder you or rob you of freedom.

It is strange that you do not commit yourself to Me with your whole heart, together with all that you can desire or possess. Why are you consumed with foolish sorrow? Why are you wearied with unnecessary care? Be resigned to My will and you will suffer no loss.

If you seek this or that, if you wish to be in this place or that place, to have more ease and pleasure, you will never rest or be free from care, for some defect is found in everything and everywhere someone will vex you. To obtain and multiply earthly goods, then, will not help you, but to despise them and root them out of your heart will aid. This, understand, is true not only of money and wealth, but also of ambition for honor and desire for empty praise, all of which will pass away with this world.

The place matters little if the spirit of fervor is not there; nor will peace be lasting if it is sought from the outside; if your heart has no true foundation, that is, if you are not founded in Me, you may change, but you will not better yourself. For when occasion arises and is accepted, you will find that from which you fled and worse.

A Prayer for Cleansing the Heart and Obtaining Heavenly Wisdom:

Strengthen me by the grace of Your holy spirit, O God. Give me the power to be strengthened inwardly and to empty my heart of all vain care and anxiety, so that I may not be drawn away by many desires, whether for precious things or mean ones. Let me look upon everything as passing, and upon myself as soon to pass away with them, because there is nothing lasting under the sun, where all is vanity and affliction of spirit. How wise is he who thinks thus!

Give me, Lord, heavenly wisdom to learn above all else to seek and find You, to enjoy and love You more than anything, and to consider other things as they are, as Your wisdom has ordered them. Grant me prudence to avoid the flatterer and to bear patiently with him who disagrees with me. For it is great wisdom not to be moved by the sound of words, nor to give ear to the wicked, flattering siren. Then, I shall walk safely in the way I have begun.

[resources: Imitation of Christ]

[Footnote from the mailbag (letter to Wall Street Journal: