Who must aggrandize Hashem?
Radak #1: Those who were at sea (and reached the dry land.
Radak #2: All four [categories that were saved from danger].
Why does it say "vi'Romemuhu bi'Khal Am"?
Rashi (from Brachos 54b): They must thank (say 'Baruch Gomel Chasadim Tovim') in front of 10.
Malbim: They will aggrandize Him to assemblies of tens of thousands in Eretz Yisrael. Romemus is for His hidden deeds. This is for commoners 1 , who do not recognize Hashem. He is elevated in their eyes.
Refer to 107:32:3:3*.
Why does it say "uv'Moshav Zekenim Yehaleluhu"?
Rashi (from Brachos 54b): Two of the 10 [in front of whom they thank] must be Chachamim.
Radak: When the Chachamim hear Hashem's wonders, they will praise Him with them (the ones who were saved).
Malbim: Tehilah is for His open deeds; this is among Chachamim 1 , who recognize His deeds.
Seemingly, even commoners recognize His open deeds, but only Chachamim recognize His hidden deeds! This requires investigation. (PF)
