Why does the Torah write "la'Chofshi Yeshalchenu" and not simply 'Chofshi hu' or 'Yeitzei Chofshi'?
Kidushin, 24a & 24b: To include the tips of the twenty-four limbs 1 that, like the eye and the tooth, are revealed and will not regrow - the fingers, the toes, the ears, the nose and the Milah of an Eved or the nipples of a Shifchah. -
Including the eye and the teeth.
Seeing as the current ruling applies to twenty-four limbs, why does the Torah mention specifically the tooth and the eye?
Rashi: Because, had it mentioned only "Ayin", we would have thought that the Din does not extend to Shen, since, as opposed to Ayin, one is not born with it. Whereas had it not mentioned Ayin, we would have thought that he goes free even if the master knocked out a milk-tooth. 1
Hadar Zekenim and Moshav Zekenim (in No'ach Bereishis, (9;25, citing the Tanchuma): Because Cham saw with his eyes and told 2 his brothers with his teeth - and was cursed with Avdus. Therefore, if one of these was stricken, he goes free. 3
So the Torah mentions "Ayin", to equate teeth to an eye, which is not destined to fall out, and "Shen", to preclude milk-teeth (Rashi).
Rosh (in Pasuk 24): He gnashed with his tooth (was upset that his father was prepared to have more sons - PF). He was cursed with Avdus, because "Ben Yechaved Av ve'Eved Adonav" (Mal'achi 1:6) - a son honors his father. If not, he will be a Eved to his master. See Rosh in No'ach, citing the Ramban.
Divrei Eliyahu: He sinned with both. Really, he should go free only if both were destroyed. It is Chesed that he goes out for one, and all the more so, afflictions, which affect the entire body, atone for him.
Why does the Torah write "la'Chofshi Yesahlchenu" and not 'la'Chofshi Yeitzei' (like it did in Pasuk 2)?
Kidushin, 24b: In order to learn a Gezeirah Shavah 'Shilu'ach' 'Shilu'ach' from Get Ishah (in Ki Seitzei, 24:3) - that the Eved requires a Sh'tar Shichrur (the equivalent of a Get).
Why does the Torah not merge Ayin and Shen into one Pasuk and conclude "la'Chofshi Yeshalchenu Tachas Eino ve'Shino"?
Bava Kama, 75b: To teach us that, if the master blinded the Eved's eye and knocked out his tooth, the Eved goes free for the eye and the master is obligated to pay for the tooth 1 (and vice versa).
Even though he had not yet received his Sh'tar Shichrur and was still an Eved when his master knocked out his tooth.