Recent scholarship has shown chattel slavery in the Roman Empire to have been a deeply oppressive experience. Paul knew that reality well and used the language of slavery metaphorically in Galatians and Romans to describe humanity's subjection to sin. However, he also made a remarkable shift in his use of the metaphor to indicate a new form of slavery to God which brings freedom, thereby subverting conventional ways of understanding slavery.
In Paul's sense, slavery is an ineluctable part of human existence in which we have a choice of being a slave to sin or a slave to God. Becoming a slave means giving up all claims to status and relates to Christ's humble-mindedness in Philippians. The slave is also a model of faithfulness, comparable with God's faithfulness to Israel and Christ's faithfulness to the mission given him by his Father. Being a slave (in Paul's sense) is at the heart of the Christian life, exemplifying the ‘obedience of faith’, for it is through this faithfulness that we become righteous.