Perkins begins by making the standard observation that Jesus' disciples, in Matthew 10, do not seem to go on mission despite their being sent on mission. (I describe this as a "standard observation" not to imply anything negative about Perkins's discussion but rather to signal that she stands firmly within the mainstream of NT scholarship here.)
Although Matthew's second discourse opens with calling and naming the Twelve as apostles to be sent on mission (10:1–5a), the Twelve do not leave Jesus' side. Instead, at the conclusion of this teaching Jesus gets up to go and preach in the towns (11:1). From a narrative point of view, that change makes the mission discourse instruction for later use, not for immediate action. (169)
But I'm not sure that this "narrative point of view" actually sheds any light on Matthew's text. First of all, in Mark's gospel the disciples do leave to go on mission (Mark 6.7, 30); should we, then, suppose that Jesus' instructions for his disciples lacked any significance or applicability for Mark's readers? Perkins does suggest this interpretation when she contrasts Matthew's Mission Discourse with "a one-time expedition while Jesus is alive" (169). Not that she says Mark 10.10–11 refers to a "one-time expedition," but she does contrast (a) Matthew's Mission Discourse with Mark's instructions for the disciples, and (b) Matthew's Mission Discourse with a one-time expedition. But I'm not at all convinced that we could read the Markan Jesus' sending the disciples out two-by-two this way, and the suggestion, even if only by implication, really isn't very helpful at all.
Second, if Mark's actual description of the disciples going out on mission does not strip Jesus' mission instructions of its significance for Mark's readers, then I'm not sure that Matthew's failure to explicitly send the disciples on mission "makes the mission discourse instruction for later use, not for immediate action." Clearly Perkins has identified a "gap" in the text, a space that the author has left unfilled and which requires the reader to supply some information in order for the story to go on. Perkins, in her reading, has filled in this gap by looking outside the text—the Matthean Jesus' Mission Discourse is directed at Matthew's readers and not at the Twelve.
John Miles Foley, however, has been arguing for nearly twenty years for the concept of "traditional referentiality," in which items explicitly within the text of an oral performance or an oral-derived text (a written text with roots in oral performance)—here Matthew's Mission Discourse—evoke items not explicitly within the text. In 1997 Werner Kelber suggested the image of a biosphere as an aid for understanding this dimension of tradition. Jesus' tradents lived within a world circumscribed by the Jesus tradition; they did not rely solely on written texts in order to access that tradition. If the gospels worked this way, rather than according to the narrowly textual dynamics according to which we gospel scholars have learned to read them, then perhaps the Mission Discourse itself signaled the disciples' missionary activity, even if the latter isn't explicitly narrated. In other words, without stripping Matthew 10 of its significance for Matthew's readers, we need not read the Mission Discourse as Matthew using Jesus' sending the disciples out "to the lost sheep of the house of Israel" (10.6) as a pretext for instructing his own readers about mission.
I must admit, however, that I'm uncomfortable with the open-ended, rather loose method of reading I'm proposing. If narrative elements outside the text governed the earliest receptions of the text, then how do we "recover" an authentic reading that is sensitive to these gaps and does not impose our own readings on the text? If I can point to something not in the text and say that Matthew wanted us to understand that it was there by means of implication, how do we determine which implications are historically appropriate and which distort the narrative? I have no answer to this except to insist on continued, close reading of the text we have. But I would notice that this problem does not escape readings such as Perkins's, either; she, too, has to "fill a gap" with extratextual phenomena. In her case, she posits a primary significance for Matthew's readers rather than for events internal to the narrative.
But the reference to "the lost sheep of the house of Israel," above, is significant, because I think Matt 10.5–6 actually supports the reading I'm proposing (namely, that the Mission Discourse itself signals the disciples going out on mission, even if Matthew doesn't explicitly narrate that mission). Perkins, because she is such a careful reader, wrestles with these verses and how they fit her reading of the discourse:
[I]f Matt 10:5b–6 articulates mission rules for later Christians, the two most vital areas of early missionary activity, Gentiles and Samaritans, are excluded. On the other hand, the Evangelist does have the risen Jesus commission his followers to go out to "all the nations" (28:16–20). . . . Exegetes are divided over how to understand that final command. (170)
This problem, I suggest, arises only because we have read the text too narrowly and without "ears to hear" the larger traditional evocations signaled by the Mission Discourse. Jesus' restrictions in 10.5–6 work within the narrative and are not Matthew's restrictions for his own readers' missionary practice. The Twelve go out on mission among "the lost sheep of the house of Israel" and not among the Samaritans and the gentiles. The text does not explicitly mention that mission because it doesn't have to; the mission already constituted part of the "traditional biosphere" in which the early Christians lived and according to which they read/heard Matthew's narrative and filled in gaps such as this.