It seems most implausible that the Didache would modify such a pervasive doctrine of the general resurrection without any explanation. However, the puzzle can be easily solved if one considers that the Didachist’s language represents an early millennialism, in which the resurrection of the righteous saints (those “in Christ”) occurs at the return of Christ, followed by an earthly reign, which then ends with the resurrection of the wicked to judgment. Though it is not entirely clear that the original eschatology of the Didache was a form of early premillennialism, it seems more historically responsible to opt for an explanation that was known in the early church (resurrection of both the righteous and the wicked separated by a millennial kingdom), rather than point to this as an instance of unique teaching regarding the resurrection of the righteous only.  - Dr. Micheal Svigel, Go Deeper: Eschatology of the Didache