There is a Medrash Pliah that states: ""The sea saw and trembled (Tehillim 114:3).' What did it see? It says Klal Yisroel coming with the bounty of Egypt in their hands."
The Blozhover Rebbe zy"a (Sefer Shufra D'Yisroel on Lag B'Omer) explains by citing the Medrash (Bamidbor Rabbah 2:22) that says that the Jewish people were taken out of Egypt in the merit of keeping a secret. Moshe told them (Shemos 3:22) that each woman should ask her neighbor for gold and silver vessels because he was planning on emptying out Egypt, and they kept this secret for 12 months, without a single person revealing it.
It is further stated in the Medrash (Bereishis Rabbah 38:6): "Shalom is so great that even if people worship idols, if there is peace amongst them, Hashem doesn't let harm befall them."
The Heavenly minister of the sea was very angry at the naton for serving dols in Egypt (see Yalkut Beshalach, Remez 234), but since the sea saw that they were coming with the bounty of Egypt, it was a proof that the nation was united and no one had revealed the secret. Thus, it trembled and did not harm them even though they had worshipped idols.
