In Friday night zemiros we say כל מקדש שביעי כראוי לו כל שומר שבת כדת מחללו שכרו הרבה מאד על פי פעלו , whoever sanctifies the seventh day as befits it, whoever safeguards Shabbos properly from desecrating it, his reward is exceedingly great in accordance with his deed.
The Chofetz Chaim offered a novel explanation on these words. There is a person who doesn’t desecrate Shabbos as he keeps its laws (כל שומר שבת כדת מחללו ). He keeps Shabbos to its minimum but it doesn’t have the spirit of Shabbos. Then there is a person who observes Shabbos the way it was meant to. He infuses the day with kedusha (כל מקדש שביעי כראוי לו). Both of these people receive great reward (שכרו הרבה מאד). However, each one according to the way he observed it (על פי פעלו).
