Exodus 20:8

זכור — This word REMEMBER which opens this commandment here and שמור “observe” which opens it in Deuteronomy (5:12) were spoken in one utterance. Similar is, (Exodus 31:14) “Everyone that profaneth it (the Sabbath) shall surely be put to death”, which apparently is in contradiction with (Numbers 28:9) “And on the Sabbath day [ye shall offer] two lambs”, a command necessitating actions which, if done for any other purposes on the Sabbath, would involve a profanation of that day. Similar is, (Deuteronomy 22:11) “Thou shalt not wear a garment of two kinds, [as of woollen and linen together]” and (Deuteronomy 22:12) “Thou shalt make thee tassels”, for the performance of which command wool and linen may be employed in combination. Similar is, (Leviticus 18:16) “The nakedness of thy brother’s wife” (the prohibition of marriage with her), and (Deuteronomy 25:5) “her husband’s brother shall come unto her” (he shall marry her). — This is the meaning of what is said (Psalms 62:12) “One thing did God speak, these two things did we hear” (Mekhilta). זכור — This word expresses the verbal action without any reference to a particular time (the infinitive), similar to, (Isaiah 22:13) אכול ושתו “to eat and to drink”; (II Samuel 3:16) הלוך ובכה “to go and to weep”; and the following is its meaning: take care to remember always the Sabbath day — that if, for example, you come across a nice article of food during the week, put it by for the Sabbath (Beitzah 16a).

זָכ֛וֹר֩ אֶת־י֥֨וֹם הַשַּׁבָּ֖֜ת לְקַדְּשֽׁ֗וֹ׃

Remember the sabbath day, to keep it holy.