What was it that they came to believe at that moment? The Maharal of Prague (Gevuros Hashem, Ch. 47) explains that they now realized that Hashem is an omnipotent G-d who could do as He wishes, and that He works through His agent, Moses.

As wondrous as the miracles they had witnessed earlier were, this one did not involve an individual river (like the Nile), but the sea itself, one of the very building blocks of creation. Only an all-powerful G-d could have accomplished this. Later, (Josh. 2:10), we find that hearing about this act was what most impressed Rachav and the people of Jericho.

Furthermore, G-d transformed something into its total opposite, the sea into dry land, an ability possessed only by the Master of the Universe. Unlike other cultures, who worshipped localized deities with specific powers, we believe in a G-d of all-encompassing power.

Actually, the Torah declares three times that Israel “believed” (Ex. 4:31, 14:31 and 17:9). Each instance represents a cardinal principle of faith: (1) G-d watches over us earthly beings, and has not abandoned His involvement in worldly affairs. (2) There is nothing in existence that is outside of His domain. (3) G-d communicated directly with us to give us His Torah. The Exodus cemented each of these cornerstones of faith.

When Moses first came to redeem Israel from Egypt, the nation affirmed their faith that G-d observed their plight, and would take care of His people. At Yam Suf, they accepted the second principle that G-d is all-powerful and can do anything. Finally, at Sinai, they believed in G-d and His Torah, the third principle.

Any skepticism regarding these principles undermines the entire faith structure. R. Yirmiya b. Elazar (Eruv. 19a) warned about three portals to Gehinnom (Purgatory), one in the sea, one in the desert and one in Jerusalem. The Maharal explains that each portal is a trapdoor for nonbelievers of the three core beliefs.

Pharaoh scoffed at G-d’s power, so he met his end in the sea, in the ultimate demonstration of that power. (Jonah thought he could escape his mission in the sea, a lesser weakness of faith, so he had to learn his lesson there.)

The desert is where the Torah was given at Sinai. Korach rejected the idea that it was G-d given, and was swallowed up by the portal in the desert.

Jerusalem represents the place and the nation on which G-d lavishes special attention. Sancheriv disbelieved this and threatened Jerusalem, so that is where he met his miraculous downfall.

Isn’t there actually a fourth cardinal tenet, asks the Maharal, retribution for the wicked after death?

Rather, he argues, this tenet is really a corollary to the first principle, that G-d watches over us and has not abandoned us. There are places on earth that are especially elevated stations of holiness. The prime example of this is the Temple, which is called G-d’s footstool (Lam. 2:1). The earthly Temple also has a heavenly counterpart (Mechilta, Beshalach 9).

Similarly, there are stations of lowliness, such as the Valley of Hinnom outside Jerusalem. There are reportedly two palm trees in this valley, between which is a rising column of smoke. As the saying goes, “Where there’s smoke, there’s fire.”  This is a portal to its other-worldly counterpart, Gehinnom.

For those heretics who refuse to believe that the souls of the wicked receive punishment after death, Jerusalem is the trapdoor to Purgatory, for it symbolizes G-d’s watchfulness over us. It would be illogical for G-d to observe evil and not hold it accountable.

Furthermore, these principles are not merely concepts for study. The Maharal observes that our

three major festivals, the shalosh regalim, correspond to and embody these three articles of faith. Passover stands for G-d’s omnipotence, culminating at the Yam Suf, Shavuos, for the giving of the Torah, and Sukkos symbolizes G-d’s continued protection of Israel.

Shabbat Shalom.