“Blessed are the pure in heart, for they shall see God.”
Matthew 5:8
Have a pure and blameless heart at all times, and you will be blessed, seeing God. The heart, in this sense, is the wellspring of who you are physically and ethically.
Your heart needs to be continually purified, as if through the cleansing effect of fire on precious metals, refining them until they have no contrary elements left.
It is like a vine that is pruned of dead, unproductive branches so that the plant has the energy and room to bear more fruit.
It is the state of being free from a mixture of false and true until only what is sincere and genuine remains.
Living in this way is what sets you apart from the rest of humanity; this is what holiness is.
The Core of the Bible 