דברים ה׳:י״ב-ט״ו

שמור. וּבָרִאשׁוֹנוֹת הוּא אוֹמֵר "זָכוֹר", שְׁנֵיהֶם בְּדִבּוּר אֶחָד וּבְתֵבָה אַחַת נֶאֶמְרוּ, וּבִשְׁמִיעָה אַחַת נִשְׁמְעוּ (מכילתא):

Preserve. In the previous [Ten Commandments] it states “remember.” [the explanation is] both of them (שָׁמוֹר וְזָכוֹר) were pronounced simultaneously and as one word, and were heard in one sound.

כאשר צוך. קֹדֶם מַתַּן תּוֹרָה בְּמָרָה (שבת פ"ז):

As . . . commanded you. Before the giving of the Torah [you were commanded to do so] at Marah.

וזכרת כי עבד היית וגו'. עַל מְנָת כֵּן פְּדָאֲךָ שֶׁתִּהְיֶה לוֹ עֶבֶד וְתִשְׁמֹר מִצְווֹתָיו:

Remember that you were a slave, etc. He freed you on the condition that you shall be His servant and preserve His commandments.