In Matthew 25 Jesus offers a riveting description of the respective fates of those who are his true disciples (the sheep) and those who are not (the goats). The key point for distinguishing these two groups comes right in the center of the passage in verse 40:
“The King will reply, ‘Truly I tell you, whatever you did for one of the least of these brothers and sisters of mine, you did for me.’
This passage has often been taken to provide an important criterion for discerning the true disciple of Jesus. The assumption is that whenever you help somebody else in the ways Jesus describes, you show yourself to be a true disciple.
Unfortunately verse 40 creates a problem with that general interpretation. Here Jesus doesn’t say that helping just anybody qualifies you as a sheep. Rather, the claim is that you are a sheep only if you help the brothers and sisters of Jesus. We can call this the “sheep criterion”.
Now obviously Jesus does not mean this in the narrow sense as if one must help his immediate or extended biological family in order to be a sheep. So then what does he mean? We get our answer in Matthew 12:50:
For whoever does the will of my Father in heaven is my brother and sister and mother.” (See also Mark 3:32-34 and Luke 8:19-21.)
We can refer to this as the BSM criterion. According to the BSM criterion, a person is a brother, sister or mother of Jesus if they do God’s will.
Finally we should note that meeting either the sheep criterion or the BSM criterion is equivalent to being a true disciple. Thus, SC=TD=BSMC.
Now for the problem. The more traditional interpretation of Matthew 25:31-46 offered a meaningful criterion for identifying sheep: they are the ones who help other people. By contrast, the interpretation of Matthew 25:40 as referring to true disciples of Jesus leads to circularity, for then a sheep is identified by the way he helps a BSM and yet a BSM just is a sheep.