Psalm 146:3-5
3 Do not put your trust in princes,
in human beings, who cannot save.
4 When their spirit departs, they return to the ground;
on that very day their plans come to nothing.
5 Blessed are those whose help is the God of Jacob,
whose hope is in the LORD their God.
Here the Psalmist just comes right out and says it, "Do not put your trust in princes." Princes could also be translated as earthly rulers. It's a broad category that could even extend to the kings of Israel.
Human beings is literally sons of humanity beginning the reference back to the Genesis creation account which he will pick up again in v. 4. But first he says that they cannot save. He doesn't have spiritual salvation in mind as we think of it today. Instead he has in mind very natural, physical forms of salvation, which he will outline in vv. 7-9.
Verse 4 furthers the allusion to the Genesis creation account. The author's use of spirit (rûah) brings to mind God breathing life into the human in the creation account as rûah literally means breath, wind, breeze. He also says that when the rulers die they return to the ground, which is yet another reference to the human being created from the dust of the ground and returning to the ground at death (Gen 2:7; 3:19). So here the psalmist is calling to mind the fleeting nature of the human being's life, even the powerful rulers. When they die their plans come to nothing.
Many commentators note the similarities in terms between this Psalm and Psalm 1 and 2. This Psalm remember is the beginning of the ending section of the book. Psalm 1 and 2 were likely originally one Psalm forming the beginning of the book. This reflects the great care, precision and genius of the psalmists crafting these psalms and organizing them. Here theme of v. 3 is found in Psalm 2 and the verb for come to nothing (abad) is also found in Psalm 1 and 2. Furthermore, the word blessed ('asre) begins the first line of Psalm 1 and begins the last line of Psalm 2.
Also notable in this text is the ver help ('ēzer). This is the same word used in the creation account to describe the creation of Eve (Gen. 2:18). Far from helper being a subordinate, demeaning term it is used most often of God being the helper to save and deliver the people of Israel (Ps. 70:5; 71:5; 121:2). It's often even used in a military context (Ex. 18:4; Deut. 33:26; Ps. 33:20). This word conveys the idea of a powerful aid, without which humanity would be unprotected and vulnerable.
In the next verses he will heap praises upon God, leaving the reader to note the obvious advantages to placing her hope in God.