Is the prodigal son a backsliding believer or a lost sinner?

Does the story of the prodigal illustrate the recovery of a swaying believer or the salvation of a lost sinner?

Most definitely the latter. The context confirms this. In Luke 15: Christ replies to the Pharisees' criticism, "This man receiveth sinners." In verses 11-32, He compares His reception of such with the father's reception of a rebellious son. These sinners, portrayed in the prodigal, were not believers who strayed, but the ungodly. To construe that this interpretation makes God the "Father" of sinners simply overburdens the allegorical framework of the parable. Describing a straying believer as "dead" though, is going too far. Also, the term "lost," as chapter Luke 19:10 shows, refers to the perishing, Further, the Savior interprets the sheep and silver as denoting 'one sinner that repenteth." Luke uses the word "sinner" 18 times, always describing the ungodly. Similarities do exist between the sinner's conversion and the saint's restoration, but some of the language true of one cannot be used of the other.

D. Gilliland