Hired service was little known anciently; slavery was the common form of service. But among the Hebrew the bond service was of a mild and equitable character; so much so that ebed, "servant," is not restricted to the bond servant, but applies to higher relations, as, e.,g., the king's prime minister, a rich man's steward, as Eliezer (Genesis 15:2; Genesis 24:2), God's servant (Daniel 9:17). Bond service was not introduced by Moses, but being found in existence was regulated by laws mitigating its evils and restricting its duration. Man stealing was a capital crime (Deuteronomy 24:7); not only stealing Israelites, but people of other nations (Exodus 21:16). The Mosaic law jealously guarded human life and liberty as sacred. Masters must treat Hebrew servants as hired servants, not with rigour, but with courteous considerateness as brethren, and liberally remunerate them at the close of their service (Deuteronomy 15:12-18; Leviticus 25:39-41). Exodus 21:2 provided that no Israelite bound to service could be forced to continue in it more than six years.
Leviticus supplements this by giving every Hebrew the right to claim freedom for himself and family in the Jubilee year, without respect to period of service, and to recover his land. This was a cheek on the oppression of the rich (Jeremiah 34:8-17). Property in foreign slaves might be handed down from father to son, so too the children born in the house (Genesis 14:14; Genesis 17:12). Some were war captives (Numbers 31:6-7; Numbers 31:9; Deuteronomy 20:14); but Israelites must not reduce to bondage Israelites taken in war (2 Chronicles 28:8-15). The monuments give many illustrations of the state of the Israelites themselves reduced to bondage by foreign kings to whom they were delivered for their rebellion. Others were enslaved for crime (Exodus 22:3, like our penal servitude), or bought from foreign slave dealers (Leviticus 25:44), so they were his property (Exodus 21:21). The price was about 30 or 40 shekels (Exodus 21:32; Leviticus 27:3-4; Zechariah 11:12-13; Matthew 26:15).
The slave was encouraged to become a "proselyte" (doulos) (Exodus 12:44). He might be set free (Exodus 21:3; Exodus 21:20-21; Exodus 21:26-27). The law guarded his life and limbs. If a married man became a bondman, his rights to his wife were respected, she going out with him after six years' service. If as single he accepted a wife from his master, and she bore him children, she and they remained the master's, and he alone went out, unless from love to his master and his wife and children he preferred staying (Exodus 21:6); then the master bored his ear (the member symbolizing willing obedience, as the phrase "give ear" implies) with an awl, and he served for ever, i.e. until Jubilee year (Leviticus 25:10; Deuteronomy 15:17); type of the Father's willing Servant for man's sake (compare Isaiah 50:5; Psalm 40:6-8; Hebrews 10:5; Philemon 2:7).
A Hebrew sold to a stranger sojourning in Israel did not go out after six years, but did at the year of Jubilee; meantime he might be freed by himself or a kinsman paying a ransom, the object of the law being to stir up friends to help the distressed relative. His brethren should see that he suffered no undue rigour, but was treated as a yearly hired servant (Leviticus 25:47-55). Even the foreigner, when enslaved, if his master caused his loss of an eye or tooth, could claim freedom (Exodus 21:6; Leviticus 19:20). He might be ransomed. At last he was freed at Jubilee. His murder was punished by death (Leviticus 24:17; Leviticus 24:22; Numbers 35:31-33). He was admitted to the spiritual privileges of Israel: circumcision (Genesis 17:12), the great feasts, Passover, etc. (Exodus 12:43; Deuteronomy 16:10; Deuteronomy 29:10-13; Deuteronomy 31:12), the hearing of the law, the Sabbath and Jubilee rests. The receiver of a fugitive slave was not to deliver him up (Deuteronomy 23:15-16).
Christianity does not begin by opposing the external system prevailing, but plants the seeds of love, universal brotherhood in Christ, communion of all in one redemption from God our common Father, which silently and surely undermines slavery. Paul's sending back Onesimus to Philemon does not sanction slavery as a compulsory system, for Onesimus went back of his own free will to a master whom Christianity had made into a brother. In 1 Corinthians 7:21-24 Paul exhorts slaves not to be unduly impatient to cast off even slavery by unlawful means (1 Peter 2:13-18), as Onesimus did by fleeing. The precept (Greek) "become not ye slaves of men" implies that slavery is abnormal (Leviticus 25:42). "If called, being a slave, to Christianity, be content; but yet, if also (besides spiritual freedom) thou canst be free (bodily, a still additional good, which if thou canst not attain be satisfied without, but which if offered despise not), use the opportunity of becoming free rather than remain a slave." "Use it" in verse 23 (?) refers to freedom, implied in the words just before, "be made free" (2 Peter 2:19).
Fausset, Andrew Robert M.A., D.D., "Definition for 'slave' Fausset's Bible Dictionary".