This is not an error of duplication. The full-fledged version of this Mitzvah are many and change for those who are learning the one/three chapter a day. The Message for the day from "Bringing Heaven Down to Earth" at the end of this Mitzvah is different than that of yesterday.

Positive Mitzvah 155: Making Shabbat holy
Exodus 20:8 "Remember the Shabbat to keep it holy"

HaShem created the world in six days.

Upon completing the creation, He declared the seventh day to be special.

He proclaimed it holy, separating it from the rest of the week by not creating anything on that seventh day - the Shabbat.

The Torah wants us to regard the Shabbat as being holy.

Just as HaShem proclaimed it to be special, we are commanded to recite a special prayer when the Shabbat arrives - the Kiddush, and when it departs - the Havdalah.

These prayers remind us of the holiness and uniqueness of Shabbat.

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To see water turn to blood, to watch as an entire sea split and stand as two walls, to be there when Joshua made the sun stand still, the laws of nature entirely abrogated... Was to perceive an infinite force that leaves no room for our finite universe.

To see G-d work miracles through nature in your everyday life, on the other hand, is to see an infinite force fitting within a finite place. Which means that He is truly beyond both finite and infinite.

From: Bringing Heaven Down to Earth by Tzvi Freeman - tzvif@aol.com