Exegesis:
en ekeinē tē hēmera ‘on that day,’ referring back to hē hēmera in v. 30, and emphatic because of its position at the beginning of the clause, even before the relative pronoun hos.
hos estai epi tou dōmatos kai ta skeuē autou en tē oikia ‘(he) who will be on the house-top/roof and his belongings in the house,’ or, removing the syntactic incongruity between the two parts, ‘whose belongings are in the house.’ For dōma cf. on 5.19.
skeuos (cf. on 8.16) here in the plural in the general meaning ‘property,’ ‘belongings,’ ‘things.’
mē katabatō arai auta ‘he must not go down (scil. into the house) to pick them up.’ arai is final infinitive and has the general meaning ‘to take,’ ‘to pick up,’ ‘to get.’
ho en agrō homoiōs mē epistrepsatō eis ta opisō ‘he who is in the field must, in the same way, not turn around to what is behind.’ The common thought of both parts of v. 31 appears to be that on the day of the Son of man there is no point in turning to, or caring about, things which might otherwise be important. eis ta opisō lit. ‘to what is behind,’ may refer either to what is behind him on the field (cf. 9.62), or to his house and what is in it. The former is preferable.
Translation:
Here again a shift to an ‘if’-clause may be preferable, cf. 9.24.
On the housetop, see “roof” in 5.19; if renderings as discussed there would suggest a decidedly abnormal place to stay, one would have to seek functional equivalent, e.g. ‘outside,’ suggesting ‘in the yard’ (Guerrero Amuzgo), with ensuing shift from ‘go down’ to ‘go in.’
With his goods in the house, or, ‘but has his belongings in the house,’ ‘but his possessions in the house.’
To be in the field, cf. 15.25.
Turn back, preferably, ‘turn around to what is behind’ (see Exegesis). ‘turn to look at/for the things he left behind’ (Sranan Tongo).
Quoted with permission from Reiling, J. and Swellengrebel, J.L. A Handbook on the Gospel of Luke. (UBS Handbook Series). New York: UBS, 1971. For this and other handbooks for translators see here . Make sure to also consult the Handbook on the Gospel of Mark for parallel or similar verses.