Psalm 146:3-4 exhorts people not to put their trust in princes and men, and it then goes on to say that men die and their thoughts perish with them. Later, in vv 7-9, we read that God judges for the oppressed, gives food to the hungry, releases prisoners, opens blind eyes, takes care of strangers, and relieves orphans and widows.
I can imagine one appealing to this Psalm to argue that we shouldn’t look to the government to help the poor or to ameliorate social problems, for God will take care of the poor, if they trust in him. We don’t need Obamacare, one may argue: those with health problems should trust in God alone to provide for their needs!
I cannot ignore that vv 3-4 exhort people not to trust in princes and human beings. A variety of historical contexts have been proposed to explain this passage. One view is that the verses reflect disappointment in the pre-exilic Judean monarchy’s failure to live up to its mandate of justice (Jeremiah 22:3).
Could vv 3-4 reflect a post-exilic setting, however? Not only have scholars observed post-exilic Hebrew in Psalm 146, but the Septuagint locates the Psalm in the time of Haggai and Zechariah. There were plenty of times in Israel’s post-exilic history when she would have become disappointed in rulers: a Persian king would be favorable to the post-exilic Jews, then a later Persian king would come along who would be unfavorable (Ezra 4). There were post-exilic Jews who had high hopes about the Jewish leader Zerubbabel, but he passed from the scene. Psalm 146:4 notes that human beings perish, perhaps as an argument for why we should not place our trust in them, but in the eternal creator God instead: a ruler may be good, but that ruler will not live forever.
I do not believe that people should check out of supporting just policies and rulers, however, for there is a lot in the Bible about societal justice and people taking concrete action to help the poor.