The first word of the possuk is וַיְהִי, which the Gemara tells us is an expression of pain. The Ohr Hachaim asks why, at a time of happiness and glee at Klal Yisroel’s great redemption and triumph, does the Torah use an expression of pain? He also asks, why does the Torah say that Par’oh sent Klal Yisroel out of Mitzrayim, was it not the Master of all actions who did so? Hashem saved us from Par’oh, why would the credit be passed on to Par’oh?
The Ohr Hachaim explains that the possuk is telling us the reason for all of the pain that Klal Yisroel needed to suffer now with Par’oh chasing after them. Was their ordeal not over yet? Hashem had forced Par’oh, with overwhelming force, to free Klal Yisroel. Par’oh announced, in no unequivocal words, that they should leave and that he had no claims against them. Why did things have to change? By chasing Klal Yisroel at the Yam Suf, Par'oh caused ruin to himself and his nation through this act. This caused pain to him and to Klal Yisroel, and that is why the Torah uses an expression of pain.
The Gemara says that the Mal’achim were about to sing praise to Hashem when He guided them through the split sea, but Hashem told them not to, saying, “the products of My hand are drowning in the sea, and you wish to sing praise?!” Hashem is not pleased when His subjects are dying, and that’s why the Torah uses an expression of pain.
The reason the exodus was painful for Par’oh was because Par’oh was the one who sent them away from Mitzrayim. If Hashem would have removed Klal Yisroel from Mitzrayim without resorting to Par’oh’s acquiescence, he would not have chased after them. He was fooled by the fact that Hashem waited for him to agree to send them and thought that he could bring them back. This caused his suffering and destruction.
The possuk then adds וְלֹא נָחָם א לוקים with a ויו at the beginning to show that this adds to the previous story. More pain was caused by the fact that they had to travel the long way around.
Another explanation offered by the Ohr Hachaim is based on the Zohar. The Zohar says whenever the Torah uses the word עָם for Klal Yisroel when referring to the Erev Rav – the mixture of nations that joined Klal Yisroel when they left Mitzrayim. When the Torah calls them בְנֵי יִשְרָאֵל, the Torah means the higher level of Klal Yisroel. The next possuk of וַחֲמֻשִים עָלוּ בְנֵי יִשְרָאֵל מֵאֶרֶץ מִצְרָיִם - And the Children of Israel went up armed from the land of Egypt is talking about those parts of Klal Yisroel.
Klal Yisroel, when they fell into the aveira of the Golden Calf, are called שחת עמך – your nation had destroyed. That was a product of the Erev Rav, not the real Klal Yisroel.
The Torah uses the word וַיְהִי, an expression of pain, when Par’oh sent the עָם out of Mitzrayim.
Hashem did not redeem the mixture of other nations from Mitzrayim, He only wanted His nation to leave Mitzrayim. It was indeed a painful experience that even those who weren’t included in Klal Yisroel left Mitzrayim. They caused problems for Klal Yisroel at every step. Par’oh sent them along with Klal Yisroel in order that they persuade Klal Yisroel to return to Mitzrayim one day.
The Torah continues with the sad story of the long sojourn in the desert, which was due to their not going the short route. וְלֹא נָחָם א לוקים דֶרֶךְ אֶרֶץ פְלִשְתִים – Hashem did not lead them on the shorter route. All this is part of the pain that was experienced when they left Mitzrayim. The reason they had to go that route was כִּי קָרוֹב הוּא – because it was close. The Ohr Hachaim explains that the Erev Rav was too close to the other side, they weren’t completely attached to the holy side. They could cause significant damage to Klal Yisroel, and they needed some time in the desert.
