Galatians 3:
27For all of you who were baptized into Christ have clothed yourselves with Christ.
28There is neither Jew nor Greek,
there is neither slave nor free man, there is neither male nor female; for you are all one in Christ Jesus.
29And if you belong to Christ, then you are Abraham’s descendants, heirs according to promise.
The same with the use in this passage from 1 Corinthians 12:
13For by one Spirit we were all baptized into one body, whether Jews or Greeks,
whether slaves or free, and we were all made to drink of one Spirit.
This is word, "slave," is used to indicate that one has no rights of their own. They are in effect the property of another.
Strong's gives this to help clarify the word in the English:
1401 doúlos (a masculine noun of uncertain derivation) – properly, someone who belongs to another; a
bond-slave, without
any ownership rights of their own. Ironically,
1401 /doúlos ("bond-slave") is used with the
highest dignity in the NT – namely, of believers who
willingly live under Christ's authority as His devoted followers.
Bill Mounce gives this:
Definition:
In the NT a person owned as a possession for various lengths of times (Hebrew slaves no more than seven years, Gentile slaves without time limit), of lower social status than free persons or masters; slaves could earn or purchase their freedom
A male slave, or servant, of various degrees, Mt. 8:9, et al. freq.; a servitor, person of mean condition, Phil. 2:7; fem. δούλη, a female slave; a handmaiden, Lk. 1:38, 48; Acts 2:18; δοῦλος, used figuratively, in a bad sense, one involved in moral or spiritual thraldom, Jn. 8:34; Rom. 6:17, 20; 1 Cor. 7:23; 2 Pet. 2:19; in a good sense, adevoted servant or minister, Acts 16:17; Rom. 1:1; one pledged or bound to serve, 1 Cor. 7:22; 2 Cor. 4:5
slavish, servile, completely controlled, as a fig. extension of a slavery system in the ancient world,
Therefore, it is important that folks understand that the word is NOT used as one who is an indentured servant who has rights and privileges in which they may exercise as a servant.
It is not appropriate to attempt to put modern connotations of the term "Indentured servant" to that of the Biblical slave.
The slaves of the Biblical accounts (both old and new testament) were far more slave then indentured servant.