To understand the concept of an unregenerate Christian we would need to consider how Martin Luther defined the word “faith.” According to Luther, at its most basic level, faith involves what Luther called notitia, which is the understanding of a proposition. Having understood the proposition what then follows is assensus. This is to assent to the proposition in question. Finally, there is fiducia, which is trust in the relevant person or thing. According to Luther all three of these layers are involved in a Christian’s saving faith.
Firstly, there is the notitia stage which would be one’s understanding of the gospel. Understanding the gospel entails that God exists, that one is morally guilty before God, that God sent Jesus to die on one’s own behalf in order to reconcile him to God, that forgiveness is provided through Jesus, and so on. Next, assensus would require one not to merely understand these things but to actually believe and place trust in them. And then in the final stage of fiducia one must place his trust in Jesus as his personal saviour so that he may be saved from sin and separation from God.
If one doesn’t feel the desire to nurture and maintain a relationship with God then it may be because he is not a regenerate Christian. One may have come only so far in faith as the stage of assensus but has not yet reached fiducia. In other words, one believes in Jesus’ resurrection and that God exists but does not have a relationship with God. However, for many fiducia is achieved through the contemplation of Jesus’ sacrificial death on the cross for mankind. Fiducia is further vitalised through how one realises that despite his own personal sin God still chose to save him.