In the parsha (31:7) Moshe gives Yehoshua Chizuk about his ability to conquer Eretz Yisrael. He says to him, "Chazak V'Ematz, Ki Ata Tavo Es Ha'Am Hazeh El HaAretz; Be strong and courageous because you will lead the people to the land." When it comes to learning Torah and enforcing the Mitzvos, Hashem tells Yehoshua (Yehoshua 1:6) "Rak Chazak V'Ematz Me'od Lishmor V'Laasos..." The pasuk uses the word "Me'od", strengthen yourself very much. Why the extra effort for Torah as opposed to conquering the land.
Rav Elyashiv in Divrei Agadah says that when it comes to Eretz Yisrael, Hashem leads us in battle. When it comes to Torah the Mishna in Avos says, "Im Ein Ani Li Mi Li?; If I am not for myself then who is for me?" When we conquer Torah and Mitzvos, Hashem wants us to lead the battle. When we are leading and manning the dangerous front lines, we need an extra measure of strength and courage to win our battles.