A Commentary, Critical, Practical, and Explanatory on the Old and New Testaments, by Robert Jamieson, A.R. Fausset and David Brown  at sacred-texts.com
1 Kings (1 Samuel) 12:1
sa1 12:1SAMUEL TESTIFIES HIS INTEGRITY. (Sa1 12:1-5)
Samuel said unto all Israel--This public address was made after the solemn re-instalment of Saul, and before the convention at Gilgal separated. Samuel, having challenged a review of his public life, received a unanimous testimony to the unsullied honor of his personal character, as well as the justice and integrity of his public administration.
1 Kings (1 Samuel) 12:5
sa1 12:5the Lord is witness against you, and his anointed is witness--that, by their own acknowledgment, he had given them no cause to weary of the divine government by judges, and that, therefore, the blame of desiring a change of government rested with themselves. This was only insinuated, and they did not fully perceive his drift.
1 Kings (1 Samuel) 12:7
sa1 12:7HE REPROVES THE PEOPLE FOR INGRATITUDE. (Sa1 12:6-16)
Now therefore stand still, that I may reason with you--The burden of this faithful and uncompromising address was to show them, that though they had obtained the change of government they had so importunely desired, their conduct was highly displeasing to their heavenly King; nevertheless, if they remained faithful to Him and to the principles of the theocracy, they might be delivered from many of the evils to which the new state of things would expose them. And in confirmation of those statements, no less than in evidence of the divine displeasure, a remarkable phenomenon, on the invocation of the prophet, and of which he gave due premonition, took place.
1 Kings (1 Samuel) 12:11
sa1 12:11Bedan--The Septuagint reads "Barak"; and for "Samuel" some versions read "Samson," which seems more natural than that the prophet should mention himself to the total omission of the greatest of the judges. (Compare Heb 11:32).
1 Kings (1 Samuel) 12:17
sa1 12:17HE TERRIFIES THEM WITH THUNDER IN HARVEST-TIME. (Sa1 12:17-25)
Is it not wheat harvest to-day?--That season in Palestine occurs at the end of June or beginning of July, when it seldom or never rains, and the sky is serene and cloudless. There could not, therefore, have been a stronger or more appropriate proof of a divine mission than the phenomenon of rain and thunder happening, without any prognostics of its approach, upon the prediction of a person professing himself to be a prophet of the Lord, and giving it as an attestation of his words being true. The people regarded it as a miraculous display of divine power, and, panic-struck, implored the prophet to pray for them. Promising to do so, he dispelled their fears. The conduct of Samuel, in this whole affair of the king's appointment, shows him to have been a great and good man who sank all private and personal considerations in disinterested zeal for his country's good and whose last words in public were to warn the people, and their king, of the danger of apostasy and disobedience to God.