Why does it say "Lachen Shim'u Devar Hashem"?
Malbim: If you want to leave Eretz Yisrael to dwell in lands other than Egypt, Hashem did not mention punishment, just you will not get the good that He promised if you will stay in Eretz Yisrael - "l'Vilti Shemo'a" (verse 13).
Why does it say "Lagur Sham"?
Malbim: The Torah warns not to return to Egypt ("va'Shem Amar Lachem Lo Sosifun Lashuv ba'Derech ha'Zeh Od" (Devarim 17:16), "Lo Sosifun Lir'osam Od" (Shemos 14:13).) Some say that the Isur is only in this way, from Eretz Yisrael to Egypt. Perhaps the Isur is only for one who leaves to live there, but not if he goes for business. If he went for business and later settled there, he did not transgress. Therefore it says "Lagur Sham."
