Calvin's commentary on Psalm 82:3:

We are here briefly taught that a just and well-regulated government will be distinguished for maintaining the rights of the poor and afflicted...According as men increase in strength, they become proportionally audacious in oppressing the weak; and hence it is that rich men seldom resort to magistrates for help, except when they happen to fall out among themselves. From these remarks, it is very obvious why the cause of the poor and needy is here chiefly commended to rulers; for those who are exposed an easy prey to the cruelty and wrongs of the rich have no less need of the assistance and protection of magistrates than the sick have of the aid of the physician. Were the truth deeply fixed in the minds of kings and other judges, that they are appointed to be the guardians of the poor, and that a special part of this duty lies in resisting the wrongs which are done to them, and in repressing all unrighteous violence, perfect righteousness would become triumphant through the whole world. Whoever thinks it not beneath him to defend the poor, instead of allowing himself to be carried hither and thither by favor, will have a regard only to what is right. We may farther learn from this passage, that although magistrates may not be solicited for succor, they are accounted guilty before God of negligence, if they do not, of their own accord, succor those who stand in need of their interference.