When you purchase a Jewish slave (Ex. 21:2)
Surely you do not purchase a slave; you purchase a man and he becomes a slave. The verse wishes to indicate that slavery does not mean complete ownership of another person. Even before he was sold he was already a slave to the Alm-ghty and must be treated with proper respect. (Alshich)
Keep away from anything false. (Ex. 23:7)
Rabbi Mendel of Kotsk used to say: It is written, "Truth sprouts from the land." But we know that nothing grows if it isn't sown first in the ground. The seeds of truth are lies; when one buries a lie in the dirt, the truth will always sprout from it.
And Moses was on the mountain forty days and forty nights (24:18)
"Not until after forty years does a person fathom the full intent of his teacher" the Talmud tells us. One day "Above" is equal to a year in this world. Moses was on Mount Sinai - "Above" - for exactly forty days and nights. Thus he was able to fully fathom Torah and wholeheartedly accept its obligations. (Ohr HaTorah, Tzemach Tzedek)
Six years shall he serve, and in the seventh he shall go free (Ex. 21:2)
"Six years" symbolizes the six thousand years of the world's existence; "shall he serve" refers to our mission to learn Torah and perform mitzvot. "In the seventh" refers to the seventh millennium, when "he shall go free," when the Messianic Era shall reign on earth and G-dliness will no longer be hidden but revealed. (the Rebbe)
And these are the ordinances which you shall set before them (Exodus 21:1)
"Before them" in every sense of the word: the Jewish people must be made to realize that My commandments are of primary concern and importance. (Rabbi Bunim of Pshishcha)