http://revach.net/article.php?id=2164

Section: Moadim   Category: Pesach
Only at Krias Yam Suf Did Bnei Yisroel Recognize Hashem?
At Krias Yam Suf the pasuk (Shemos 14:31) says “VaYaaminu B’ashem”; Bnei Yisroel believed in Hashem.  Were Yetzias Mitzrayim and the ten makkos not convincing enough for them?  The Bais HaLevi teaches us an important yesod.  He says that all that happened in Mitzrayim was punishment for the Mitzrim for their brutal treatment of Bnei Yisroel.  Bnei Yisroel in their own right was not ready for the geula since we were supposed to wait 400 years and only 210 years had elapsed.  It was simply the overzealous oppression on the part of the Mitzrim that got them in trouble and as a side effect led to our early redemption.  The ten makkos were punishment for them, as nature changed its course to rein terror on Mitzrayim and avenge their cruelty.  We however had no zechus in which to be redeemed.  We were no angels ourselves.  This is why we were told to stay indoors during Makas Bechoros, since we had no merit with which to be spared Hashem’s fury.

Krias Yam Suf was quite the opposite. We already had the mitzvos of Mila and Korban Pesach to our credit.  The entire basis of the miracle was not Hashem’s revenge on Mitzrayim; rather it was mercy on us who were facing annihilation while trapped on the bank of the sea before a bloodthirsty enemy.  Hashem did a Nes that was pure rachmanus, as he changed Maasei Bereishis to allow us to pass through the raging waters.  The death of Mitzrayim was not the Nes.  That was simply the result of people trying to walk through a stormy sea.  No big surprise that they ended up dead.  

The Nisim in Mitzrayim were revenge or din, which is represented by the name Elokim.  That is the powerful Hashem we saw in Mitzrayim.  However on the Yam Suf we saw an all merciful Hashem who changed nature to save his beloved children.  Not only that, but we also witnessed how an all merciful Hashem can use his mercy to kill and destroy our enemies.  That was a concept that Bnei Yisroel never knew existed.  Only at Krias Yam Suf did the Bnei Yisroel see the great hand of “Hashem” the merciful, and not in Mitzrayim.