Siyum Hashas, Nida 73a

תנא דבי אליהו כל השונה הלכות בכל יום מובטח לו שהוא בן העולם הבא שנאמר (חבקוק ג) הליכות עולם לו אל תקרי הליכות אלא הלכות:
What is so important of being "shoneh halachos" every day?  Learning Mishna Brura Yomis?  And why is the reward so great - assured of being a ben Olam haba? 

Now, Shoneh means recite Torah Shebal Peh - see Shabbos first perek ( & Tana D'Vei Eliyahu Perek 15) See end of my post here).  So I think the pshat is Shoneh Halachos means "study halachos l'Moshe Misinai"  because they are Torah Shebal Peh, and studying it every day shows a lot of dedication.  So if you are very dedicated to studying these Halachos LeMoshe Misinai, which are absolute Torah Shebal Peh, you are committing to Torah min Hashmayim and Mesorah, so the reward is Olam Haba, which is something that only exists because of the Mesorah - Olam Haba is not in Torah shebiksav.  That is why this is the reward.