The translation ‘servant’ spares the harshness of the Hebrew and Greek words for a slave, and modern translations often prefer the reality. As such, the OT ‘servant’ possessed no legal rights though he was admitted to membership of the covenant people (Gen. 17: 12) and observed its basic laws (Deut. 12: 18).
In the NT Jesus speaks of people as servants of God, i.e. wholly given to his service. Jesus can himself accept this role of extreme humility (Mark 10: 45). Matt. (12: 18–21) quotes the first Servant Song (Isa. 42) as a portrait of Jesus, and Paul's words in Phil. (2: 7) seem to echo Isaiah; so Christians are also to be servants of each other (John 13: 14) because they are servants of Christ (1 Cor. 7: 22).