From Ohr Avigdor Hakdama by Rabbi Avigdor Miller
Among the positive mitzvos of the mind are . . .
1. To believe the world has a Creator. To believe the world has a Creator is clearly a mitzvah for the mind. We don’t fulfill this mitzvah simply by saying we believe. We must feel it; we must have an inner conviction that Hashem created the world.
2. To believe that He created it out of nothingness. It is not that He found materials and created the world from them, but that He created the materials too. The world is existence made out of non-existence (yesh me’ayin). This is a mitzvah of the Torah, which the author discusses at length in Chapter 1 (Shaar Hayichud).36 It is a mitzvah to have the thought in our conscious mind that Hashem created the world out of nothing.
A person who observes Shabbos but doesn’t think about the fundamental principle of Shabbos is missing the point
The day of Shabbos was made so that you should be able to devote time to thinking that Hashem created the world out of nothingness. Of course, the obligation to devote time to this mitzvah applies throughout the week as well, but especially on Shabbos. A person who observes Shabbos but doesn’t think about the fundamental principle of Shabbos is missing the point.
When he says " a remembrance of the act of creation," (Shabbos Kiddush and Shemoneh Esrei) he should consciously dwell on the idea that Hashem created the world from nothingness. That is, in fact, the most fundamental concept of Shabbos. If you think about it for a minute that’s an achievement. If you think about it more than a minute it’s an even bigger achievement. You should always remember that the thinking about Creation is a fundamental purpose of what Shabbos is all about.
Whenever you stop and think about the fact that Hashem made the world out of nothingness, that there was nothing and then it became reality, you have fulfilled a mitzvah, just as if you have put on tefilin, or as if you sat in the sukkah or put a mezuzah on the doorpost.
The more we utilize Shabbos for that purpose, the more our minds develop and the more the attitude and conviction that the world is made out of nothingness becomes ingrained in us. It is worthwhile emphasizing this point. It’s an example of how people are accustomed to saying things without assimilating what they are saying and without making it a part of their personality.