Samuel's ministry was not over. He saw that his responsibilities were winding down though. And so, in his goodbye speech to the nation, Samuel asked the people if he had wronged them in any way as their judge. He knew that he hadn't. And, they knew that he hadn't. So, Samuel ended his political ministry with a clear conscience.
He still had a significant amount of spiritual duties remaining though. Even in this oration Samuel was preaching righteousness to his people. Despite their sin in seeking for a human king (to take God's place) as their leader, Samuel promised that God would bless them if they would simply obey Him from then on (I Samuel 12:14). Samuel even called for God's verification of his words. He called for God to send rain on that day. It was a time in the summer when it never rained in that region. The Mediterranean climate there in the Holy Land has a winter rainy season offset by hot, dry summers. But, at the word of Samuel, God sent a mighty rain storm that day which brought great fear into the hearts of the people. Not that the storm was scary, but the people feared God and Samuel because of their obvious command over the forces of nature.