יְׂשַלֵם ה' פָעֳלֵךְ וּתְׂהִי מַשְׂ כֻרְׂ תֵךְ שְׂ לֵמָה ב יב
Just For Accepting the Torah, A Person Receives Automatic Schar Forever
The Malbim explains that there are two forms of Schar. Besides for the Schar you get every time you do a Mitzva, when a person is M'kabel (accepts on himself) to keep the Torah (like Rus, who was M'gayer) he automatically receives a: שכר תמידי perpetual Schar for the rest of his life! So on Shavuos, when we are M'kabel the Torah, we should realize that there is an ongoing Schar for the rest of our lives, as a reward for this Kabala (acceptance).
It is important every Shavuos to look at yourself like a new person, as if you were a Ger, and to appreciate our holy Torah more and more. In all probability, the more you value the Torah, and the happier you are at Zman Kabolas HaTorah, the more constant Schar you'll be getting forever.
People tend not to appreciate their greatness, and this is a trick of the Yetzer Hara (Chovos Halvavos) since the more Simcha and value that you give your Kabala (acceptance), the more Zechus and the more unending lifetime Schar! So keep saying and remarking: אַשְׁרֵינוּ מַה טּוֹב חֶלְקֵנוּ “How fortunate is our lot!" that we are Zoche to be M'kabel the Torah. And for every tiny ounce of Simcha and appreciation, the more we are Zoche, with Hashem’s help.
