The sixth beatitude (Matthew 5:8): "Blessed are the pure in heart, for they shall see God." Greek katharoi tē kardia — katharos means "clean, unalloyed, unmixed" (as of metal without dross, or milk without water added), and kardia is the biblical center of will, affection, and thought. The beatitude echoes Psalm 24:3-4: "Who shall ascend the hill of the LORD? And who shall stand in his holy place? He who has clean hands and a pure heart."
Purity of heart is single-mindedness toward God. The pure heart is not divided between God and rival loyalties — not half-hearted, not hypocritical, not playing at religion for show. It is not sinless perfection (no one meets that standard this side of glory), but it is undivided orientation. "Pure" contrasts with "double-minded" (James 4:8 — "Cleanse your hands, you sinners, and purify your hearts, you double-minded"). Søren Kierkegaard's meditation Purity of Heart Is to Will One Thing unpacks the beatitude at length: the saint wills one thing — the Good, God Himself — and all lesser things are subordinated to that single aim. The hypocrite wills many things, which is why He cannot see God; His vision is scattered and refracted. The promise — "they shall see God" — is the beatitude's stunning reward. No one has ever seen God (John 1:18); sinners cannot see God and live (Exodus 33:20). Yet the pure in heart shall see Him. Present sanctification purifies the vision; the consummation gives us the face-to-face beholding (1 John 3:2 — "we shall see him as he is").