Katharos (without admixture) means clean, pure, unstained, either literally or ceremonially or spiritually; guiltless, innocent, upright. Early on in the exegesis of the Fathers of the Church we see the three fundamental directions in which the beatitude of purity of heart will be received in the history of Christian spirituality delineate themselves: the moral, the mystical and the ascetic.
The moral interpretation emphasizes rectitude of intention, the mystical interpretation emphasizes the vision of God, and the ascetic interpretation emphasizes the struggle against the passions of the flesh. In reality, purity of heart does not indicate, in Christ’s thinking, a particular virtue, but a quality that should go along with all the virtues, so that they are truly virtues and not rather “glittering vices.” Its most direct contrary is not impurity, but hypocrisy. What Jesus means by “purity of heart” is made clear by the context of the Sermon on the Mount. According to the Gospel, what determines the purity or impurity of an action — whether it be almsgiving, fasting or prayer — is the intention: Is the deed done to be seen by men or to please God?
Nature and dignity 