My 4-year-old has this game where I have to copy his varied facial expressions. He smiles, I have to smile; he starts to frown, and I immediately have to copy that. Even though it’s a game, I find it almost natural; my facial expressions naturally start to mirror his.

G‑d works the same way. He responds to us, almost naturally, and prayer is where it all happens.

But let's take a step back to see why that happens specifically during prayer and also get a deeper understanding of why prayer is so necessary. Why can’t doing mitzvahs and being a nice guy suffice as service of G‑d? Why the need for such a seemingly abstract, lofty and spiritually demanding form of service called prayer?

In order to answer these questions, let’s review a core tenet discussed often in the study of Chassidus:

Our sages say that “one hour of repentance and good deeds in this world is better than all the life in the World to Come” (Avot 4:17). That’s why it says that G‑d “placed [Adam] in the Garden of Eden to cultivate it and guard it” (Genesis 2:15). Man contributes to the Garden of Eden and cultivates it, drawing down a more powerful light than is possible to access in the spiritual worlds.

How is the above accomplished? Through the dynamic duo: the combination of repentance and good deeds. This is not just referring to repentance for sin but rather one hour of repentance, that earnest desire to return to G‑d felt during prayer and good deeds—the tangible mitzvahs tethering the great light—are together greater than all the life of the world to come.

Prayer is what accesses and draws down this intense great light of G‑d, while doing a mitzvah grounds the great light into a physical vessel that can contain it. This transforms this physical world into a holy home for G‑d, a place where He can be comfortable. This is literally the reason you are here, living your life, and the reason G‑d created you: to pray and do mitzvahs, and to upgrade the world for Him.

This is illustrated in the fact that service, prayer, is associated with the phrase yaakov avdi, “Jacob my servant.” The name Yaakov as it is spelled in the Hebrew has a deeper meaning relating to prayer. Yaakov starts off with the letter yud, which is a small letter, like a dot. The remaining three letters spell another word, the Hebrew word eikev, which means “heel.” The dot represents G‑d’s essence, and the heel, as the lowest part of the body, represents the lowly physical world where G‑d wants His essence to shine.

And that is what prayer is all about. Just like the spinal cord carries brain signals from the brain, which eventually gets down even to the pinky toes and the heel, prayer draws down from the “yud,” G‑d’s essence, and reveals the light into this physical world.

And now we are back to the original question. But why? What quality does prayer have that draws down this great light? Why is prayer so needed to draw down G‑d’s essence?

And here is the answer: because prayer is the time when G‑d reflects our “facial expressions.” The goal of prayer is to express the true desires of the heart which is to reveal G‑dliness to the world. A person operates on many levels, with actions, speech and thought. But there is something deeper than thought and intellect: a person’s raw desire. Prayer is about arousing a sincere and raw desire for G‑dliness, and expressing our soul’s desire to connect and be one with G‑d. This intense desire of the heart, or reusa di’liba, is what causes G‑d to naturally reflect back. The longing to have a relationship with G‑d, above intellect, is what causes a natural drawing down of His great light and essence, which is above intellect.

This is the special quality that prayer has and why it is so crucial to our purpose in life. In fact, this service of Jacob is so great that it is said: “He has not seen iniquity in Jacob”—sin, or iniquity itself, is scared off and intimated by this great light generated by “Jacob”—drawing down light into this physical world.

Prayer is where we cement that relationship and G‑d mirrors our desire, and we draw down G‑d’s desire and light. Only then do we follow it by doing mitzvahs and bringing that special yud into the “heel,” the physical and mundane world and make a home for G‑d.

Through prayer, we draw down G‑d’s essence, unleashing the great light and establishing the reflection in the relationship. Like a parent to a child.

Soul Note: My sincere desire for G‑d arouses Him to reflect His essence back to me.

Source: The Maamar, lo hibit avon biyakov, in Likkutei Torah as explained in Chassidut Mevueret, Chapters 5 and 6