This verse mentions three people who for one reason or another have left Paul.
For: in some languages it will be helpful to follow Revised Standard Version‘s model and keep the For in For Demas, to show the connection with the previous verse. Paul needs Timothy because both Demas and Crescens have left him for various reasons, and only Luke remains with him (compare verse 11).
The name Demas also appears in Col 4.14 and in Philemon 24, where he is identified as Paul’s fellow worker. Whether the Demas in 2 Timothy is the same Demas mentioned in Colossians and Philemon is difficult to ascertain. It may be simply incidental that the names are the same. At any rate, if these references refer to the same people, then Demas may have deserted Paul at a later time.
The word for world is also the word that is sometimes translated “eternity.” Here the focus is on the world as transitory and under the influence of evil, and therefore opposed to God. The world is characterized as present as opposed to the coming world. This also contrasts Demas with Paul and all those who long eagerly for Christ’s appearing. See further comments on 1 Tim 6.17.
Deserted translates a verb that means “to leave behind,” in either a good or a bad sense; in the present context it is definitely the negative sense that is in focus. In certain languages this will be expressed figuratively; for example, “threw me away” or “discarded me.” It is not clear as to whether this desertion is simply physical (Demas left Rome) or spiritual as well (Demas left the Christian faith). Since Paul does not explicitly say that Demas has renounced the Christian faith, it is best to focus simply on the fact that Demas had left Rome and gone somewhere else. In certain languages it will be helpful to say “left me here in Rome and went….”
For gone to see “going to” in 1 Tim 1.3.
Thessalonica is the capital city of the Roman province of Macedonia, which is now northern Greece. In the book of Acts we are told that Paul established the church there (see Acts 17.1-9; see also the map, page 6|fig:Map_Paul-12.jpg).
Crescens appears only here in the whole New Testament. There is no other information about him.
Galatia most probably refers to the Roman province in southern Asia Minor by that name (presently part of Turkey). It is in that part where Paul went during his first missionary journey (see Acts 13.13–14.26; 15.36–16.5; note the route on the map, page 6|fig:Map_Paul-12.jpg).
Titus, a Gentile Christian, was one of Paul’s co-workers and is prominently mentioned in many of Paul’s letters. He accompanied Paul to Jerusalem (Gal 2.1) and played an important role in the correspondence between Paul and the church at Corinth (see 2 Cor 2.13; 7.6). In Titus 1.5 we are informed that Paul left Titus behind in the island of Crete. He was probably also known as Silas (see Acts 15.40; Gal 2.1).
Dalmatia occurs only here in the whole New Testament. It consists of the southern half of the province of Illyricum (present-day Albania) on the northeast coast of the Adriatic Sea. See Rom 15.19.
Quoted with permission from Arichea, Daniel C. and Hatton, Howard A. A Handbook on Paul’s Second Letter to Timothy. (UBS Handbook Series). New York: UBS, 1995. For this and other handbooks for translators see here .