Why does the Torah repeat that Yisrael went into the sea?
(14,22) “And the Children of Yisrael came into the midst of the sea on dry land; and the water was a wall for them, on their right and on their left.”
Behold, in posuk 29 it says “and the Children of Yisrael went on dry land into the midst of the sea; and the water was a wall for them on their right and their left”. Why does the Torah tell us again that the Children of Yisrael went into the sea. And since the Torah says that they went on dry land, the fact that “the water was a wall for them on their right and their left” seems to be an unnecessary repetition of this fact. And why does our posuk say that they went “in the midst of the sea on dry land”, but here it changes the order and says “on dry land in the midst of the sea”? Also, in the later posuk the word חומה (wall) is written without the letter 'vav' - and Chazal expound on this and teach that Hashem was filled with anger (חמה) against the Children of Yisrael.
But everything can be explained by the fact that there were at that time two groups. There were the Tzaddikim who believed and trusted in Hashem, and who immediately went into the sea until the water was a threat to their lives - as we see from the Midrash which teaches that Nachshon ben Aminadav jumped into the sea, followed by the entire tribe of Yehudah. But the others waited until there was dry land before they entered the sea.
Now, the Midrash teaches that there was an accusation against Yisrael that they were no better than the Egyptians since they both worshiped idols. But Hashem replied to the accusation that the merit of their belief and trust in Hashem was sufficient for them that they should be saved.
According to this, with regard to those who went immediately into the water, believing and trusting in Hashem, it says “and the Children of Yisrael came into the midst of the sea” and then they went “on dry land”, and so they deserved that “the water was for them a wall (חומה)” to protect and to save them. But the second group who were lacking in faith and waited until they saw with their own eyes the dry land, about them the Torah writes that “they went on dry land into the midst of the sea”. Therefore, “the water was for them חמה”, that is, against them was the accusation that they did not deserve be saved.