Van de Sandt, Huub. "Chapter Ten: Two Windows on Developing Jewish-Christian Reproof Practice: Matt 18:15-17 and Did. 15:3." in Van de Sandt, Huub (editor). Matthew and the Didache: Two Documents from the Same Jewish-Christian Milieu? Minneapolis: Fortress Press, 2005, 173-192.
A relationship between Matthew 18:15-17 and Didache 15:3 is often posited due to the emphasis on confession and the Didache's reference to "the gospel," taken to be Matthew's Gospel (Van de Sandt 2005, 173). Van de Sandt compares the passages, also evaluating a "parallel in the Manual of Discipline (1QS)" (Van de Sandt 2005, 174).
Van de Sandt first evaluates Matthew 18, the fourth extended discourse found in Matthew (Van de Sandt 2005, 174). The start speaks of children being welcomed to Jesus, then the passage continues speaking of childlike behaviors. In verses 15-20 the passage moves on to confrontation and attempts at conflict resolution in case of sin. Forgiveness is the focus, as Jesus emphasizes in verses 21-22, telling his disciples to forgive "seventy times seven" times. He follows with a parable of an unforgiving servant (Van de Sandt 2005, 174). The majority of the material in the context parallels a passage in Luke 17, however, van de Sandt takes verses 15-20 not to exist in the Q source, as they are not found elsewhere. He does note the close connection to Leviticus 19:17 and the express intention of confrontation leading to reconciliation. Matthew 18:15-17 shows a judicial concern, with the specific conditions clearly spelled out (Van de Sandt 2005, 176). The negative reference to "pagans and tax collectors" also strikes van de Sandt as out of character with other statements in Matthew (Van de Sandt 2005, 177).
Van de Sandt continues by comparing the reproof passage in Matthew with that in Didache 15:3 (Van de Sandt 2005, 178). The passage in Didache 15 is clear that the reproof is directed to "a brother" and is thus friendly in nature. The goal is repentance so as to be restored to the eucharist. Unlike the passage in Matthew, the Didache passage has no hint of a judicial regulation (Van de Sandt 2005, 179). The function of witnesses is important in Matthew, while it is not present in the Didache.
Van de Sandt next makes a comparison with two reproof passages found in the Qumran material (Van de Sandt 2005, 180). Though van de Sandt finds judicial practices evidenced in rabbinic law, the reproof passages are intended as warnings against sin, rather than confrontations after the fact. A warning was to be issued and proven to have been issued prior to the transgression so as to allow any judicial process to be taken up. Van de Sandt details a number of the judicial intricacies (Van de Sandt 2005, 181ff).
The reproof passage of 1QS 5:23b-6:1b calls for reproof as necessary prior to presentation of an offender to the elders (Van de Sandt 2005, 184-185). It is to be conducted in front of witnesses, counter to the Matthew passage which requires a private setting at first. While there are procedural steps, it does not necessarily have a judicial impact. Rather, van de Sandt takes it as part of a routine examination of community members. There were judicial procedures clearly spelled out in other passages. This leads van de Sandt to conclude that the passage in Matthew, with specific instructions for confrontation as well as a judicial process was influenced by the Qumran community in some way (Van de Sandt 2005, 186).
Compared to Matthew, the reproof in Didache 15:3 is entirely consumed with a desire for reconciliation. The goal is clearly nothing other than reconciliation (Van de Sandt 2005, 187). The reference to "the gospel" is not entirely clear. However, van de Sandt considers it very unlikely that the passage would be derived from Matthew 18. It may be a reference to something influenced by the 1QS material. This view may be strengtehend by the fact that the 1QS narrative refers to a regular review of character. This is more similar to Didache 15 than to Matthew 18 (Van de Sandt 2005, 189).