‘Blessed are the pure in heart,’ says God, ‘for they shall see God’ (Matthew 5:8). But purity of heart cannot be realized through one virtue alone, or through two, or ten; it can only be realized through all of them together, as if they formed but a single virtue brought to perfection.
Even so the virtues cannot by themselves purify the heart without the presence and working of the Spirit. For just as the bronzesmith demonstrates his skill through his tools, but cannot make anything without the activity of fire, so a man using virtues as tools can do everything given the presence of the fire of the Spirit; but without this presence these tools remain useless and ineffective, not removing the stain that befouls the soul.
~St Symeon the New Theologian
Prayerful Life 