What is the meaning of Rabbi Shimon bar Yochai's assurance that in the merit of the book of Zohar, we will be redeemed from exile with mercy?

There are two concepts in Chassidic philosophy that describe our Divine service to hasten the Redemption. The two are “War” and “Peace.”

Whenever one uses a physical object to perform a mitzvah, one is waging war against the forces of impurity. Every physical object has a G-dly spark hidden inside it, which the powers of impurity can divert for their own sustenance. When one uses the G-dly force inside the object for a holy purpose, the powers of impurity are cut off of their source of life, and the object is restored to its original spiritual source. The object itself becomes holy. It is clear that the forces of impurity do not desire this outcome and therefore they wage a battle, which expresses itself in the various obstacles that a Jew encounters on the way to perform a mitzvah. When a Jew overcomes these challenges, he weakens the forces of impurity.

However, there is also a more direct route. This is simply to increase the powers of holiness, in a peaceful manner. When one studies Torah, particularly the inner dimensions of Torah, one causes G-d to shine forth His light from the highest levels of holiness. This, as a matter of course, weakens the powers of impurity, without their putting up a direct fight.

The Torah and its inner dimensions are compared to a bubbling spring. Moshiach told the Baal Shem Tov in a vision that he would appear when "Your wellsprings will spread outward." When the wellsprings of the inner dimension of Torah will spread forth to all areas of the world, Moshiach will arrive.

This is the meaning of Rabbi Shimon bar Yochai's promise, that in the merit of the wellsprings of Torah as expressed in Zohar, upon which the teachings of Kabbalah and Chassidus are based, we will go out of exile with mercy, in a peaceful manner.

Zohar vol. 3, 124b, Raya Mehemna. Keser Shem Tov. Toras Menachem 5745, vol. 1, p. 805