Rashi in his commentary says that this refers to certain specific commandments given at that time, including Shabbat.
Ahad Ha'am famously said: “More than the Jews have kept the Sabbath, the Sabbath has kept the Jews.” Indeed, we refer to strict Shabbat observance as “keeping shabbat”, being “shomer Shabbat” - meaning to “guard and protect”, but there are actually two dimensions.
In the two different versions of the fourth commandment which appear in the Torah, the first uses zachor – “remember”, the second shamor – “keep”. This is also a reason for lighting two Shabbat candles. Zachor represents the positive mitzvot and observances of Shabbat, shamor the negative mitzvot and restrictions.
When we sing Lecha Dodi on Friday nights, we say it the other way round “Shamor v’zachor” – first the negative, then the positive. Why the change in sequence?