Unceasing prayer was enjoined by God Himself. The Savior of the world said, ‘Ask, and it will be given you; seek, and you will find; knock and it will be opened to you.’ ‘And shall God not avenge his own elect who cry out day and night to Him, though He bears long with them? I tell you that He will avenge them speedily.’
…in order to become eventually capable of unceasing prayer [one] must practice frequent prayer. Frequent prayer in due time passes automatically into unceasing prayer….
He who does not train himself to frequent prayer will never receive unceasing prayer. Unceasing prayer is a gift of God, given by God to a slave and servant of His of proven fidelity. ‘It is impossible to draw near to God other than by unceasing prayer.’ (St Isaac the Syrian)
Unceasing prayer is a sign of God’s mercy toward a man; it is a sign that all the powers of his soul are bent on God.
~Ignatius Brianchaninov
Prayerful Life 