From D.A. Carson:
The kingdom of heaven requires poverty of spirit, purity of heart, truth, compassion, a nonretaliatory spirit, a life of integrity; and we lack all of these things. Then let us ask for them! Are you as holy, as meek, as truthful, as loving, as pure, as obedient to God as you would like to be? Then ask for grace that these virtues may multiply in your life! Such asking, when sincere and humble, is already a step of repentance and faith, for it is an acknowledgement that the virtues the kingdom requires you do not possess, and that these same virtues only God can give. Moreover, I suspect that this asking, seeking and knocking has a total package as its proper object. It does not seek holiness but spurn obedience; it does not seek obedience but hedge when it comes to purity. It is a wholehearted pursuit of the kingdom of God and his righteousness. And this pursuit is stamped by stamina: it is a persistent asking, seeking, knocking.
(Jesus’ Sermon on the Mount and His Confrontation with the World, p. 117)