I Samuel - Chapter 12
The Rain in Israel Falls Mainly on the Wheat
Now that Shaul had been crowned king, Shmuel was ready to withdraw from his role as Judge. (He would still serve as prophet, but he was no longer the head of the government or the military.) Shmuel asked if anyone had any complaints against him; nobody did. Shmuel then reminded the people that it was G-d Who sent Moses and Aaron, and Who saved them from Egypt. But when the nation forgets G-d, He allows foreign powers like Sisera and the Philistines to oppress them. However, when the people return to G-d, He sends redemption through great leaders (and less-than-great leaders). Here Shmuel named the lesser Judges: Gideon, Samson and Yiftach. The Talmud in Rosh Hashana, daf 25b, top, says that these leaders were as appropriate for their generations as Moses and Aaron were for theirs. Speaking prophetically, Shmuel was impelled to include himself in the list of leaders of the Jewish people, doing so in the third person.
However, Shmuel still maintained that the people erred in demanding a king to lead them, rather than Hashem Himself. The fact that G-d had granted their request was no proof that it was necessarily a good thing, as Shmuel would proceed to demonstrate. It was summer, when it doesn't rain in Israel, and the wheat was standing in the fields. Shmuel called out to Hashem and a heavy thunderstorm rained down (which wasn't a good thing for the crop). The people were afraid that they had sinned by asking for a king and they asked Shmuel to pray for them. He told them not to worry, just to continue by listening to the Word of Hashem. If they follow Hashem, they will be His people. If they stray, both they and the king they requested are done for.