We could not bear it any longer must refer to the intense emotion which Paul and his colleagues felt in missing the Thessalonians. It may be necessary to make this reference more specific, for example, “we could not endure any longer not seeing you,” or, stated idiomatically, “our being away from you was crushing us.”
The word so is important because it introduces clearly the reason for the decision. In some languages this reason may need to be made explicit, for example, “because of how we felt.” Or the preceding sentence may be combined with this statement about the decision, for example, “At last, because we could not endure any longer being away from you, we decided….”
We decided is the same verb which in 2.8 is translated we were ready, but here the tense shows that Paul is not thinking of a state of being ready and willing, but of a specific decision. This is not brought out by Revised Standard Version (“we were willing”), Le Nouveau Testament. Version Synodale (“we preferred”), or Traduction œcuménique de la Bible (“we thought it best,” cf. Zürcher Bibel). Decided is rightly chosen, not only by common language translations, but by Knox Barclay Translator’s New Testament (cf. Luther 1984 Jerusalem Bible). Moffatt has the equivalent “made up my mind” (cf. La Sainte Bible: Nouvelle version Segond révisée Bible de Jérusalem).
In translating we in verses 1 and 2, it is important to make the proper transitions and to indicate clearly who is involved. This will mean that in many languages the first “we” in verse 1 will be the exclusive first person plural to include Paul, Silas, and Timothy. The second “we” will be the same (“we decided”), but the implied third “we” must refer merely to Paul and Silas, for the two of them were the ones who stayed on alone in Athens. Therefore it may be necessary to translate “so we three decided that we two would stay on alone in Athens.” The we of we sent would then refer to Paul and Silas, but our in the phrase our brother would be inclusive first person plural (for languages having the inclusive-exclusive distinction), since Timothy would be a fellow believer, not only of Paul and Silas, but of the Thessalonians as well. Us in the phrase who works with us would again refer simply to Paul and Silas. Only a careful sorting out of precise references in the use of we, our, and us can prevent serious misunderstanding.
To stay on is passive in form, literally “to be left behind” (Revised Standard Version), but the context shows that Paul is writing from his own point of view, not that of Timothy. Good News Translation and most other translations make this clear by the use of “remain” or the more common equivalents “stay on” or “stay behind” (Translator’s New Testament).
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 .