זָכוֹר - Imbuing the Mitzvos with Passion
We can complete our duties of the positive commandment to sanctify the Shabbos, by simply following the letter of the law. However, the kedushah that comes from this kind of avodah, is minimal. In order to maximize the untold levels of sanctity that can be generated through honoring the Shabbos, one must perform every mitzvah with great kavanah and passion.
The Chafetz Chaim cites the zemer of Kol Mekadeish that we sing on Friday night where we say that everyone who keeps the Shabbos according to halachah, receives great reward, עַל פִּי פָּעֳלוֹ - according to his actions. He points out that the reward - the kedushah that one merits, is entirely commensurate with a person's deeds. The more one honors the Shabbos, and invests thought and kavanah into every mitzvah, the greater reward he will merit עַל פִּי פָּעֳלוֹ.
(חפץ חיים עה''ת)
