Radak: One may, as long as his primary trust is in Hashem, that He will put in the person's heart to help him. One must avoid "u'Min Hashem Yasur Libo" (Yirmeyah 17:5).

Malbim: It is a Mitzvah not to trust even in Nedivim, even though he wants to do good and normally does so, for two reasons. Refer to 146:3:2:2, 146:4:1:2.

Radak: The matter is repeated in different words. If Hashem does not want, one cannot save another. Salvation is only from Hashem; He causes it via people, e.g. salvation of Galus Bavel via Koresh. Also in the future, He will cause Ge'ulas Yisrael via kings of the nations. He will arouse their spirit to send them - "v'Hevi'u Es Kol Acheichem mi'Kol ha'Goyim Minchah la'Shem" (Yeshayah 66:20). This will be because Yisrael trusted in Hashem in Galus.

Malbim: Since he is human, the power of salvation is not his; it is not in him.