7. The Hebrew word for slave, ‘ebed, can speak of literal slavery to a human master. But it is also used metaphorically to describe believers (more than 250 times), denoting their duty and privilege to obey the heavenly Lord. The New Testament's use of the Greek word, doulos, is similar. It, too, can refer to physical slavery. Yet it is also applied to believers—denoting their relationship to the divine Master—at least 40 times (cf. Murray J. Harris, Slave of Christ [Downers Grove, IL: InterVarsity Press, 1999], 20-24). An additional 30-plus NT passages use the language of doulos to teach truths about the Christian life. 

8. See, for example, Romans 1:1; 1 Corinthians 7:22; Galatians 1:10; Ephesians 6:6; Philippians 1:1; Colossians 4:12; Titus 1:1; James 1:1; 1 Peter 2:16; 2 Peter 1:1; Jude 1; and Revelation 1:1. 

9. According to the International Standard Bible Encyclopedia (hereinafter referred to as ISBE), some commentators have proposed that the term "Christian" literally means "slave of Christ." For example, "Deissmann (Lict vom Osten, 286) suggests that Christian means slave of Christ, as Caesarian means slave of Caesar" ( John Dickie, "Christian," in James Orr, ed., ISBE [Chicag Howard-Severance Company, 1915], I:622). 

10. Stringfellow Barr, The Mask of Jove (Philadelphia: Lippincott, 1966), 483. 

11. Northcote, Epitaphs of the Catacombs, 140. 

12. Karl Heinrich Rengstorf, under "δοῦλος," in Gerhard Kittel, ed.; Geoffrey Bromiley, trans., Theological Dictionary of the New Testament, vol. 2, notes that, "In the early Church the formula [slave of God or slave of Christ] took on a new lease of life, being used increasingly by Christians in self-designation (cf. 2 Clem. 20, 1; Herm. m. 5, 2, 1; 6, 2, 4; 8, 10, etc.)" (Grand Rapids: Eerdmans, 1964, 274).

13. In a second-century letter from the churches of Lyons and Vienne to the churches of Asia and Phrygia, the anonymous authors began by designating themselves the "slaves of Christ" (Eusebius, Ecclesiastical History, 5.1-4). They continued by describing the widespread persecution they had endured, including the martyrdoms that many in their midst had  experienced.

14. As Janet Martin Soskice explains, "Talk of the Christian as ‘slave of Christ' or ‘slave of God' which enjoyed some popularity in the Pauline Epistles and early Church is now scarcely used, despite its biblical warrant, by contemporary Christians, who have little understanding for or sympathy with the institution of slavery and the figures of speech it generates" (The Kindness of God: Metaphor, Gender, and Religious Language [New York: Oxford University Press, 2007], 68).

15. For example, Rengstorf notes the prominence "in the NT [of ] the idea that Christians belong to Jesus as His δοῦλοι [slaves], and that their lives are thus offered to Him as the risen and exalted Lord" (Theological Dictionary of the New Testament, s .v. "δοῦλος" 2:274).

16. Even earlier, John Wycliffe and William Tyndale rendered the Greek doulos with the English word "servant."

17. According to Harris, "this word [doulos] occurs 124 times in the New Testament and its compound form syndoulos (‘fellow-slave') ten times" (Slave of Christ, 183). The verb form also occurs an additional eight times.

18. Two exceptions to this are E. J. Goodspeed's The New Testament: An American Translation (1923) and the Holman Christian Standard Version (2004), both of which consistently render doulos a s "slave."