Purity of Heart Is to Will One Thing was written by Søren Kierkegaard in 1846 and is part of his Edifying Addresses of Varied Tenor. The central focus of Kierkegaard's philosophy (and in particular of this work) is the individual. He starts out by setting out man as an individual in relation to the Eternal. Following the biblical book of Ecclesiastes, Kierkegaard says that there is something eternal in man that needs to exist, regardless of his mortal nature. He then continues:

But the Eternal is that which is set over all, The Eternal will not have its time, but will fashion time to its own desire, and then give its consent that the temporal should also be given its time.

The temporal is subject to the Eternal, and man needs to be in the right relationship with the latter in order to truly be an individual. Because man is trapped in the temporal and is not a true individual before a relationship with the Eternal is established, the way to establish this relationship, according to Kierkegaard, is through remorse, repentance, and confession. However, these actions cannot be limited to the temporal:

But repentance shall not have its time in a temporal sense. It will not belong to a certain section of life as fun and play belong to childhood, or as the excitement of love belongs to youth. It will not come and disappear as a whim or as a surprise. No, remorse should be an action with a collected mind, so that it may be spoken of to the edification of the hearer and so that new life may be born of it, so that it does not become an event whose sorrowful heritage is a feeling of sadness.

Rather than being a religious ordinance, an outward rite, or even a repeated action of a heart, remorse is put forward by Kierkegaard as an inner disposition that leads the true individual to stand before the Eternal. Much more than simply feeling penitent about a misdeed, it must be a concentrated determination of the individual's will grounded in a consciousness of the Eternal.

Considering the Apostle James's words about single-mindedness as a prerequisite for an effectual prayer, Kierkegaard concludes:

For only the pure in heart can see God, and therefore, draw nigh to Him; and only by God's drawing nigh to them can they maintain this purity. And he who in truth wills only one thing can will only the Good, and he who only wills one thing when he wills the Good can only will the Good in truth.

Here the thinker makes this "one thing" to be desired equal with the Good. This willing is not to be confused with desiring something—because an object of desire can be coveted whether it is good or bad. Kierkegaard argues that to long for something to the point of despair would mean being "double-minded"—being uncertain and wavering back and forth between desires—and only by willing Good can the individual not be uncertain or waver, since the Good is pure and singular (and thus affords no possibility of wavering). Every thing other than the Good is not a unity but rather a multiplicity—which is why willing something other than the Good causes the "double-minded" uncertainty and means that there is no purity of the heart.

There are, however, many obstacles to willing this one thing and thus to being pure in heart. Kierkegaard argues that there are false wills that corrupt this purity, such as willing out of fear of punishment, self-seeking service of the Good, as well as not...