Why did Hashem command Yisrael to go back towards Egypt?
Rashi: To trick Pharaoh into believing that they were lost - to encourage him to chase after them. 1
What is the significance of Pi ha'Chiros?
And what is the significance of Ba'al Tz'fon?
See Sifsei Chachamim.
Moreover, it had succeeded in trapping Yisrael beside the Yam-Suf, for his army to attack - another means employed by Hashem to lure Pharaoh and his army to the Yam-Suf (Refer to 14:2:1:1*), as the Pasuk writes in Iyov (12:23) "He tricks the nations and destroys them (Rashi, citing the Mechilta). The Seforno (in Pasuk 5) adds that they erred in not first consulting Ba'al Tz'fon before sending Yisrael away - and Paroh and the Egyptian army now came to bow down to it and to praise it (Targum Yonasan [Refer also to 14:10:13).