The keys to three of Hashem's treasure houses were not placed in the hands of any agent, states Rabbi Yochanan. The keys to rain, childbirth and resurrection of the dead are held by Hashem alone.
Tosefot poses the challenge that the key to rain was given to the Prophet Eliyahu (Masechta Sanhedrin 113a) which enabled him to declare (Melachim I 17:1) "during these years there shall be no dew or rain save upon my word." Tosefot's resolution is that this was only a temporary transfer of power.
Rashi seems to have anticipated this challenge by explaining that all three keys have never been placed in the hands of an agent at one time. This is a subtle reference to what the aforementioned gemara describes as the aftermath of Eliyahu's withholding rain to punish an idol-worshipping country and king.
Immediately after a passage describing the drying up of the nation's water supply, another passage relates that Hashem commanded Eliyahu to go to the home of a widow in the city of Tzorfat where he was soon faced with the challenge of resurrecting her dead child (Melachim I 17:7-22).
There is a connection, our Sages say, between these two events. When Hashem decided that the people had suffered enough from Eliyahu's withholding of rain, He arranged for Eliyahu to be placed in a situation of attempting resurrection. Eliyahu prayed that Hashem give him the key to resurrection so he could restore life to the child of the widow who had shown him so much hospitality.
Hashem's response was that He alone had control of the three aforementioned keys, and the one to rain had already been given to the prophet. If Eliyahu were to receive the key to resurrection as well, it would result in the absurd situation of two keys being in the hand of the servant and only one in the hand of the Master. Eliyahu was thus compelled to return the key to rain, and the next chapter (Melachim I 18:1) begins with Hashem restoring rain to the land.
Source: From the Weekly Daf by
Rabbi Mendel Weinbach zt’l
MORE ON THE THREE KEYS
Ben Yehoyada (Scribd): The keys refer to the power given by Hashem to “nature” to provide activities in the world. However, these three keys refer to acts that defy nature. (According to the laws of physics, it is impossible for the dead to be resurrected. Similarly, rainfall (and weather in general) follows no natural physical, predictable laws. It is not likesunrise and sunset or the motions of the planets and celestial bodies which can be predicted thousands of years in advance. In this sense, rainfall is "supernatural"and demonstrates the presence of the Creator more than any other event. Similarly the process of conception and birth are not set functions.) These three “keys”, the ability to cause the activities, remains in HaShem’s hands.
Screenshot from Scribd: