This is holiness. This Beatitude Praises, not a specific action, but a habitual condition of the spirit, a state of being. Leiva is getting at the heart of Christian moral life here. This habitual condition or state of being is what the great scholastics called habitus. For the scholastics the term habitus indicated a dynamic vision of the human person, because man is a creative being who is open to growth and transformation from the acquired and infused virtues.
Human actions change our being.
Vices also form our character. For example, when we steal we make ourselves thieves. The pure of heart have their reason, will and emotions in a state of harmony. The pure heart follows the path of the Beloved because it sees that fulfillment rests on pursuing Christ's way. The heroism the Lord asks of his disciples is not based on abstract ideology.