For someone who desires spiritual rebirth, the first step towards the light is to curtail the passions, that is to say, to guard the heart; for it is impossible otherwise to curtail the passions. The next stage is to devote oneself to psalmody; for when the passions have been curtailed and laid to rest through the heart’s resistance against them, longing for intimate union with God inflames the intellect. Strengthened by this longing the intellect repulses all distractive thoughts that encircle the heart, attempting to get in, and it rebuffs then through attentiveness. So it applies itself assiduously to the second stage, that of attentiveness and prayer. This then stirs up the evil spirits, and the blasts of passion violently agitate the depths of the heart. But through the invocation of the Lord Jesus Christ they are utterly routed and all the tumult melts like wax in the fire. But though they have been driven out of the heart the demons continue to disturb the intellect externally through the senses. However, because they can only trouble it superficially, the intellect soon regains its serenity; none the less, it can never by completely free from the attacks of the demons. Such freedom is to be found only among those who have attained full manhood — who are totally detached from everything visible and who devote themselves unceasingly to giving attention to the heart. After that, those who have achieved attentiveness are raised little by little to the wisdom of old age, that is to say, they ascend to contemplation; and this is the stage of the perfect.
Thus if you practise all this in due sequence, completing each phase at the right time, your heart will first be cleansed of the passions, and you will then be able to concentrate wholly on psalmody; you will be able to wage war against the thoughts that are roused by the senses and disturb the surface of the intellect and you will gaze heavenwards, if need be, alike with your physical and your spiritual eyes, and will pray in true purity. Yet you should gaze upwards only occasionally because of the enemies that lie in ambush in the air.
God asks only this of us, that our heart be purified through watchfulness. As St. Paul says, if the root is holy, so also will the branches and the fruit be holy (cf. Rom. 11:16). But if without following the sequence of which we have spoken you raise eyes and intellect to heaven in the hope of envisaging noetic realities you will see fantasies rather than the truth. Because our heart is still unpurified, as we have said many times, the first and the second methods of attentiveness do not promote our progress. When we build a house we do not put on the roof before laying the foundations — this is impossible. We first lay the foundations, then build the house, and finally put on the roof. We must do the same in relation to spiritual matters. First we must lay the spiritual foundations of the house, that is to say, we must watch over the heart and curtail the passions arising from it. Then we must build the walls of the spiritual house, that is to say, though the second form of attentiveness we must repulse the turbulence of the evil spirits that fight us by means of the external senses, and must free ourselves as quickly as possible from their attacks. Then we must put on the roof, that is to say, detach ourselves entirely from all things and give ourselves wholly to God. In this way we complete our spiritual house in Christ Jesus our Lord, to whom be glory throughout all the ages. Amen.
Excerpt from Philokalia: The Three Methods of Prayer attributed to St. Symeon the New Theologian