Paul’s use of figurative language raises several problems here. First, there is a transition from the Day in the sense of an unknown time at which God will bring history to its climax, to the day (v. 5) as an image of the openness of Christian living. This transition is indicated in Good News Translation by capitalization of Day in the first sense, but this device is inadequate to convey the distinction to anyone who only hears the passage read aloud. The second sense of day is well established by verse 5. The implication in verse 4 is that Christians have nothing to fear from that final Day in which everything will be known and judged, because they already live lives in which there is nothing to hide.
Second, the image of a thief reappears in a sense which cannot be defined until a decision is taken about the meaning of the word translated take … by surprise. This verb, in the meaning required by the context, may include the following elements: (1) being seized, so that one cannot escape; (2) being overtaken or surprised (as a traveler in Mediterranean latitudes could be overtaken unexpectedly by the sudden arrival of night); (3) suffering harm. All elements fit the present context well, but which is the translator to choose as central? (1) takes up the idea expressed in verse 3b, (2) reverts to the idea of verses 2-3a, and (3) takes up the thought of verse 3a (destruction). Most translations agree with Good News Translation in taking (2) as central, and this may well be correct. However, (1) is the common meaning of the verb where the context does not define it in some other way (but compare John 12.35).
If the translator chooses such an expression as “seize” or “catch,” he must be careful to make the two terms of the comparison clear. The meaning would not be: “the Day should not catch you as a thief is caught,” but “the Day should not seize you as a thief seizes someone” (for example, the occupant of the house he is about to rob).
The relation between the two parts of this verse is left open or implicit by Good News Translation (cf. Bible en français courant), which links them only by and. The relation indicated by the Greek is one of reason and result, for example, “you are not in darkness, and so you should not be surprised…,” or “since you are not in darkness, you should not be surprised….”
You … are not in the darkness is a figurative expression, and as such it may be difficult to render literally in some languages, since darkness may have nothing to do with either ignorance or the wrong kind of life. It may be important to change this metaphor into a simile, for example, “but you do not live as it were in the darkness,” or “… in the night.” One may also translate as “but you do not live as those who are ignorant of God and who sin.”
It is impossible to say in some languages “the day will take you by surprise,” since surprise is not something that a person experiences with regard to a particular day. Therefore, one may need to restructure this latter part of verse 4 to read “and therefore you will not be surprised when the day of the Lord comes, as a thief might surprise someone when he (the thief) grabs him.”
Quoted with permission from Ellingworth, Paul and Nida, Eugene A. A Handbook on Paul’s First Letter to the Thessalonians. (UBS Handbook Series). New York: UBS, 1976. For this and other handbooks for translators see here .