הַמַּכֶּה רַק שִׁבְתּוֹ יִתֵּן וְרַפֹּא יְרַפֵּא
"he shall, however, pay for his lost work-time, and he shall provide for his cure. [Mishpatim 21:19]
A man once came to R' Baruch Mordechai of Koidanov. Signs of intense suffering were etched on the man's face.
"Rebbe", said the man, "I have been suffering terribly for a long time. Please give me a bracha that I should recover from my illness."
"I will give you some advice" responded the Rebbe. "Be extra careful to avoid Shabbos violations, and try your utmost to honor the Sabbath. Do so and Hashem will grand you a speedy recovery."
The man did as the Rebbe had instructed. Shortly thereafter, the excruciating pain that he had been feeling began to subside. Finally, it went away altogether.
"Do not think that I performed a miracle" the Rebbe later told his students. "It is a 'treatment' that the Torah itself recommends, as the verse states: "Rak shivto yiten v'rapo yerapei'. The word 'shivto' can also be read "shabato", meaning "his Shabbos". The verse can therefore be read as follows:
"Let him give his Shabbos, and he will surely be healed."
That is, if a person pay attention to his Shabbos observance and honors it properly, then Hashem will provide him with a complete recovery.
Source: Rabbi Yisrael Bronstein