From The Art of Prayer – An Orthodox Anthology
Sometimes we pray by using the words of prayers already composed; at other times prayer is born directly in the heart, and from there rises to God. Such was the prayer of Moses before the Red Sea. The Apostle refers to it in the words, “By grace, singing in your heart to the Lord.” Explaining this text, Saint John Chrysostom writes: “Sing from the grace of the Spirit, says Paul, not simply with the lips but with attention, standing with your thought before God in your heart. For this is what singing to God means: otherwise the song is in vain, and the words vanish into thin air. It is not sung to show off, for even if you are in the market place, you can turn to God within and sing, without being heard by anyone. It is good to pray in the heart even when traveling, and be lifted on high.” Only this kind of prayer is real prayer. Oral prayer is prayer only in so far as the mind and heard also pray.
This prayer is formed in the heart by the grace of the Holy Spirit. He who turns to God and is sanctified by the sacraments, immediately receives feeling towards God within himself, which from this moment begins to lay the foundation in his heart for the ascent on high. Provided he does not stifle it by something unworthy, this feeling will be kindled into flame, by time, perseverance, and labor. But if he stifles it by something unworthy, although the path of approach and reconciliation to God is not thereby closed to him, this feeling will no longer be given at once and gratis. Before him is the sweat and work of seeking and of gaining it by prayer. But no one is refused. Because all have grace, only one thing is necessary: to give this grace free scope to act. Grace receives free scope in so far as the ego is crushed and the passions uprooted. The more our heart is purified, the more lively becomes our feeling towards God. And when the heart is fully purified, then this feeling of warmth towards God takes fire. Even in those who have ceased for a time to experience the working of grace, this warmth towards God revives long before they have arrived at a complete purification from passions. It is still only a seed or a spark but when it is carefully tended, it glows and begins to flame. Yet it is not permanent, but blazes up and then dies down, and in its burning is not of even strength. But no matter how dimly or brightly it burns, this flame of love always ascends to the Lord and sings a song to him. Grace builds up everything, because grace is always present in believers. Those who commit themselves irrevocably to grace, will pass under its guidance, and it shapes and forms them in a way known only to itself.