Through prayer we have the power to channel G-d’s providence in a way that goes beyond nature. Nature may dictate one thing but prayer has the power to change nature.
Yehoram, king of Israel, said to Gehazi, “Please tell me the great things that Elisha did” (II Kings 8:4), for “Whatever Elisha did, he accomplished through prayer” (Megilah 27a).
Thus prayer, which gives us access to the realm of miracles and providence, the very opposite of nature, is “great.”
Avraham Greenbaum, The Essential Rabbi Nachman