Génesis 26:12 Comentario: Rashi, Rashbam, Sforno & Or HaChaim

בארץ ההוא IN THAT LAND although it (Gerar) had not the sacred importance of Erez Yisroel proper — i. e., as the territory of the seven nations, and is therefore not as fertile as the Holy Land (cf. Ketubot 112a).

בארץ ההיא, even though the soil of this land is exceptionally hard;

ויזרע יצחק בארץ ההיא, in accordance with G’d’s instructions “גור בארץ הזאת” (verse 3)