What object, one might ask, could be so valuable that its theft could equal the price of a person's life? (And remember, Torah law goes to great lengths to avoid actually carrying out capital punishment.) Additionally, if the Eighth Commandment prohibits simply stealing, then what is the purpose of the Tenth Commandment, which prohibits coveting, but is only truly violated if one actually acts to obtain the coveted item illegally?
Questions such as these, along with a subtle analysis of the language, lead the sages to understand that this particular injunction is actually intended to mean "thou shalt not kidnap," a capital crime. (However, other verses in the Torah, and the very detailed civil code of the oral law, make it clear that ALL theft is prohibited. It just isn't a capital crime.)
What is so serious about the act of kidnaping that it merits inclusion in the Ten Commandments? Central to God's creation of humankind is His gift of free-will. Slavery is permitted in the Torah because the slave becomes a slave through his own actions (stealing, enemy in war). When a person steals another person, however, the victim unjustly loses the important human element of freedom.
In a situation where a kidnaping has occurred, Jewish law places tremendous weight on the act of redeeming the captive. Rabbah ben Mari explained (Talmud Bava Batra 8b) that captivity is worse than natural death, sword and famine, and therefore the redemption of captives is a religious duty of the greatest importance.
Maimonides (Rabbi Moses ben Maimon/Rambam Spain/Egypt/Israel 1135 - 1204) wrote that the act of pidyon shevuyim, redeeming the captive, was part of three different mitzvot in the Torah: 1) "you shall not harden your heart" (Deuteronomy 15:7); 2) "you shall not stand idly by the blood of your brother" (Leviticus 19:16); and 3) "you shall love your neighbor as yourself" (Leviticus 19:18).