The day in this passage may well refer to the day of the Lord (as in 1 Thess 5:2; see Cullmann 1950:43). Such a warning prevents suffering believers from building up undue expectations that would set them up for exploitation (Mt 24:23-27); this sort of warning was especially critical in view of the tendency of many of Jesus' contemporaries to predict signs of the end (see comment on 24:6-8).

Like the flood, the Son of Man's coming (Dan 7:13-14) would arrive as sudden and unexpected judgment, without explicit warning. Jesus' followers might recognize the completion of requisite signs (compare 1 Thess 5:4-6), but for outsiders, life would be business as usual (banquets and weddings, or grinding with a hand mill). This passage echoes the damnable folly of outsiders repeated throughout the Gospel tradition in general and Matthew in particular (as in 13:19; 15:10): they do not understand (24:27, 39). If Jesus means "taken in judgment" (Jer 6:11; 8:13; compare Ps. Sol. 13:11), the "taking" parallels the different expression in Matthew 24:39, where the flood took the wicked away (see Lk 17:34-37; contrast Sirach 44:16-17).

Keep watch does not mean "look for" or "anticipate immediately," but borrows the image of a night watchman at his post (Mt 24:42; 25:13; Ladd 1974b:208): the believer must remain prepared for the Lord's coming, remaining alert and awake (26:38, 40-41, 43-46). That the time of Jesus' coming is unknown does not preclude that some signs mentioned earlier in the passage will precede it (compare Gundry 1982:491-92; Katterjohn and Fackler 1976:118-19), any more than such ideas were incompatible in various ancient Jewish end-time views (see, for example, Bonsirven 1964:53). The early Christians often reused Jesus' image of a householder unprepared for a nocturnal thief (compare Joel 2:9) for Jesus' return at the end (1 Thess 5:2, 4; 2 Pet 3:10; Rev 3:3; 16:15).