Note: The Sfas Emes notes that this ma'amar is a continuation of the ma'amar he said on the first night of Shavuos. This ma'amar can be understood independently. To see the ma'amar that he said the first night click here.
The first time the ten commandments are mentioned in the Torah at the giving of the Torah, we find, “זָכוֹר אֶת־יוֹם הַשַּׁבָּת .../Remember the Shabbos day …” (Shmos 20:7) Forty years later, when Moshe repeats the story of the acceptance of the Torah he says, “שָׁמוֹר אֶת־יוֹם הַשַּׁבָּת .../Keep the Shabbos day …” (Devarim 5:12) Why the change from זָכוֹר/Remember to שָׁמוֹר/Keep? Moshe Rabbeinu certainly did not change what God said. Chazal tell us that God said, and we heard, both זָכוֹר/Remember and שָׁמוֹר/Keep simultaneously. Why, though, did God say both “Remember” and “Keep”, and what is the significance of saying them simultaneously?
The mitzvah of keeping Shabbos actually comprises both a positive and negative commandment. זָכוֹר/Remember, refers to observing the positive commandment of Shabbos. שָׁמוֹר/Keep, refers to the prohibitions of Shabbos. This explains the two wordings, however, it does not explain the significance of God having said them simultaneously.
In order to understand this, we need to reach a deeper understanding of זָכוֹר/Remember and שָׁמוֹר/Keep. In order to refrain from transgressing the admonition against violating the Shabbos, we need to be concerned about it. Negative commandments are generally associated with fear or awe whereas positive commands are associated with love. The feeling of fear or awe which prevents us from transgressing prohibitions corresponds to the concern which keeps us in a state of preparedness for performing mitzvos with love. שָׁמוֹר/Keep, therefore is more than a reference to the prohibition against violating the Shabbos. It implies a state of preparedness.
זָכוֹר/Remember on its highest level is not really remembering at all. Rather it is a connection to something at such a deep level that it becomes a part of us to the extent that there is no possibility of forgetting. It is a connection to our innermost essence. This is a very high level that not everyone merits reaching. In fact, it is a level of Godly revelation. Chazal are teaching us that a person who is careful about שָׁמוֹר/Keep – a person who keeps prepares, can be granted a level of זָכוֹר/Remember on its highest level.
God said them simultaneously because as soon as we reached a level of completeness implied by שָׁמוֹר/Keep, God granted us the revelation implied by זָכוֹר/Remember.
In addition to God saying both words at the same time, Chazal tell us that we heard them as well, something that is impossible in nature. How, then, could this be and what is the significance of it? The answer to this question involves a deeper understanding of what Torah is. As we’ve said elsewhere, Torah is much more than scrolls with words written on them. In fact, Torah is primarily a spiritual force which was enclothed in physical trappings in order to bring it into the physical world. This is what Chazal mean when they say that the Torah is both hidden and revealed. Chazal, in fact, teach us that the Torah’s descriptions of spiritual events or entities in physical terms are not accurate. The Torah is simply using terms to which we, as physical beings living in a physical world can relate more easily.
It follows that on a physical level, we can see only the physical trappings of the Torah, its plain meaning. However, when we recognize that the Torah that we see is only the wrapping, allegories for the spiritual Torah, and subordinate ourselves to that spiritual Torah, not just to the outer wrapping, we can merit hearing the inner secrets of the Torah, things that cannot be heard physically. The nation reached this level at the giving of the Torah. At that time the Torah tells us that we saw sound. This is an allusion to experiencing that part of the Torah which cannot be experienced on a physical level. We were on a level at which the spiritual Torah was being revealed to us.
This also explains the deeper meaning behind, “זָכוֹר וְשָׁמוֹר בְּדִיבּוּר אֶחָד נֶאֱמְרוּ/Remember and Keep were said at the same time (lit. with one speech).” As a watchman – שׁוֹמֵר – guards from the outside, שָׁמוֹר implies keeping the plain meaning of the Torah. זָכוֹר implies understanding and connecting with the hidden mysteries of the Torah. The Hebrew for speech – דִיבּוּר – implies revelation as the Sfas Emes explains elsewhere regarding the עֲשֶׂרֶת הַדִיבְּרוֹת/ten commandments. Because of God’s revelation we were able to hear both the physical plain meaning of the Torah and spiritual deeper meaning at one and the same time.
 There are divisions and levels to our souls. At the highest spiritual level our souls connect with all the souls of the nation of
 Zohar 3:72b
 Tanchuma Yisro 13
 Sfas Emes Bo 5631 First Ma’amar