Blessed are the pure in heart, for they shall see God.
The first three Beatitudes, before the blessing for those who hunger and thirst after righteousness, correspond with the three that follow that blessing. The poor in spirit are merciful to others in their condition. Those who mourn over sin seek a new heart (to be pure in heart) (Psalm 51:10). Those who are meek tend to be peacemakers.
Christ blesses those who are pure in the heart; not the head.
The heart is the center of the personality. More than just the seat of the affections and emotions, it is the total man – the core of his being.
A pure heart is unified (single) in its devotion to God (Romans 7:21-25 and Psalm 86:11).
Purity of heart is a strong proof that Christianity is, in fact, supernatural. The heart of natural man is anything but pure (Genesis 6:5 and Jeremiah 17:9). Only God can give man a pure heart (Deuteronomy 30:6; Ezekiel 36:26).
Holiness, a pure heart, and an unmixed condition of being are necessary for one to see God. Also, as with so many other things in our Christian walk, this is an example of already/not yet. The believer sees God in everything, all of creation, now. The unbeliever sees Him in nothing. The believer will also see God face-to-face, and he will spend eternity in His presence.