Why will they rejoice?
Malbim: They will see that You save those who trust in You.
Malbim (40:17): Mevakshei Hashem are unlike those who seek something else. The latter is happy about the request only if he gets what he wanted. Seeking Hashem is itself the purpose!
Who are "Mevakshecha"?
Radak: They are people who request only Your salvation, and not from others.
Why will they say "Yigdal Elokim"?
Radak: This is like Gadol Elokim. He shows His Gedulah to Ohavav and saves them from [enemies] greater than them.
Radak (40:17): When He does miracles and Chasadim, He is Gadol.
Malbim: He constantly does new miracles.
Why does it say "Ohavei Yeshu'asecha"?
Malbim (40:17): One who does not love the salvation itself, only that the affliction ended, he would prefer that there was no Tzarah and no need for salvation. Those who love the salvation, for it brings Kidush Hashem, they want to constantly need salvation, for then there is constantly Kidush Hashem!
