Rabbi Ami teaches that it is due to the merit of people who truly believe in God that rain falls. The source for this teaching is Tehillim 85:12, according to which truth grows from the earth and righteousness comes down from the skies.
Continuing with the theme of those who truly believe, Rabbi Ami points to the story of those who believe in the hulda u-bor – the marten (a rodent) and the pit – arguing that if you believe in the hulda u-bor, certainly you can believe in God.
It is interesting that the Gemara feels no need to explain what the story of the hulda u-bor entails, taking for granted that it was a story so well known that there was no need to put it in writing. Rashi and Tosafot both tell a short version of the story, but a lengthier version, whose source is in the traditions of the Ge’onim, appears in the Arukh.
As R. Natan ben Yehiel tells it in his Arukh, the story begins with a girl from a noble family who loses her way and, having fallen into a well while drinking, cannot manage to extract herself. A passerby hears her cries and shouts. After a lengthy conversation during which time he ascertains that she is, in fact, a woman and not a demon of some sort, he agrees to save her, on the condition that she will marry him. Upon lifting her from the well he wants to consummate the marriage immediately, but she objects, arguing that a Jewish man surely wants to marry according to the halakha and would not be interested in simply fulfilling animalistic urges. They agree to marry and appoint the well and a passing weasel as witnesses to their pact.
Upon returning home, she scrupulously kept her agreement, refusing the entreaties of all suitors. He, on the other hand, soon forgot the agreement and married another woman, who bore children – the first of whom was bitten by a marten, the second of whom drowned in a well. Seeing that her children died under unnatural circumstances, she demanded an explanation from her husband, who admitted that he had promised another that he would marry her. They divorced and he searched for the woman who he had saved and promised to marry. When she refused him – as she did all others – he told her of the honest witnesses, the hulda u-bor,that brought him back to her. In the end they married and had many children, proving the passage in Tehillim (101:6) that God’s eyes are upon the faithful who merit a close relationship with Him.