"To love G‑d, your G‑d, with all your heart" (Deuteronomy 11:13); "which is the service of the heart? It is prayer."

This terse definition of prayer as the "service of the heart," quite adequately covers its meaning.

The heart is the central organ which controls the blood-circulation, the very flow of life.

On the metaphysical level, the heart is also the medium through which humanness expresses itself. In the heart are ignited the sparks of human feelings and passion. From it flicker the flames of human desires and caprices, and through its manifestations we perceive man's character and personality.

From the heart springs life to all limbs, for from it flows the stream of blood to all the limbs, to the very end of the body, and from the same heart stem the ascending and conjoining aspirations of the soul to its source in G‑d.

Little wonder, then, that G‑d says to man: "Give Me your heart. For when your heart is Mine, then I know that you are Mine!"

This, then, is the general idea of prayer: the service of man's heart.

It means a complete, unconditional surrender of the self to G‑d: becoming so bound up and united with G‑d that one perceives
only the Divine aspect in everything.

Prayer is the direct, undisturbed communication with G‑d, the channel bringing us to the reality of unison with the true Essence of all.

This definition is actually implied in the Hebrew term for prayer: tefilah.

The word tefilah is derived from a root-word that means to join together, to unite.

Tefilah sets out to join and unite man and G‑d, creature and Creator, to permeate the former with the radiance of the Latter. This is accomplished only when tefilah is the true service of the heart: with proper devotion and concentration; involving the totality of man - every part of the mind, absorbing all thoughts and feelings.

If the mind does not fully partake, the bond is loose and incomplete. Man remains exposed to the danger of extraneous thoughts intruding and interfering.

That kind of prayer is like a roofless - thus insecure - courtyard: defenseless against any downpours of harmful rains.

Total involvement is the first and foremost condition for prayer.

It is the meaning of "to love G‑d and to serve Him with all the heart," with all one's being; to surrender oneself completely, to dissolve in the unity of the bond with thoughts or desires for nothing else.

In the metaphorical terminology of the Kabbalah and Chassidism, therefore, this proper form of prayer is spoken of as a zivug, a figurative state of marital union, the offspring of which is new conceptions, new love and reverence for G‑d.

These effects result from consciousness of the Divine, in each person on his or her own level, corresponding to the individual efforts in prayer.