Shared ground
These closing lines bring Psalm 108 to a clear conclusion: the speaker asks God for help against a real enemy, and then states why that request must be directed to God. “The help of man is vain” makes a blunt claim that human support cannot secure the needed rescue.
The next verse combines human action with divine action. Explicitly, the speaker expects “we will do valiantly” through God, and also that God himself will “tread down our enemies.” The confidence is grounded in what God will do, not in the strength or reliability of human allies.
Where interpretation differs (only where needed)
Some readers take “the help of man is vain” as denying the value of any human assistance in principle. Others read it more narrowly: human help may have a role, but it is not dependable as a final source of deliverance.
Some also hear “through God, we will do valiantly” as strong cooperation (God enables, the people fight), while others stress dependence (any effective action only happens because God empowers and decides the outcome).
“Tread down our enemies” is usually read as battle language, but some take it as a broader image for God decisively defeating threats, not necessarily limited to a single military scene.
Why the disagreement exists
The key phrases are poetic and compressed. Words like “vain” can mean “useless,” “unreliable,” or “unable to bring victory,” and the phrase “through God” can imply different shades of relationship between divine help and human effort. In addition, “tread down” is vivid imagery, and imagery can be read more literally or more broadly.
What this passage clearly contributes
The text explicitly contributes a two-part conclusion: (1) a direct petition for God’s help against enemies, paired with a judgment that human help cannot deliver; (2) renewed confidence that effective action (“do valiantly”) and the final defeat of enemies belong to God’s agency. It portrays reliance on God as the decisive basis for hope in conflict and threat, with human effort described as enabled “through” God rather than independent from him.