First Timothy 1-6, Second Timothy 1-4, Titus 1-3, Philemon

First Letter of Paul to Timothy is, as it suggests, a letter from Paul to his favorite associate.  He's asking Timothy to remain in Ephesus.  He also warns about dissenting ministries, explains his past. Paul also outlines a number of guidelines for the emerging Church, including rules for the selection of bishops of deacons.  It's more or less a set of instructions to keep on keeping on.

Second Letter of Paul to Timothy finds Paul missing Timothy.  He's hit a rough patch.  The ministries in Asia have been less than accommodating.  He tells Timothy not to be ashamed of testifying and to accept suffering, which might just as well be Paul telling these things to himself, which in effect makes this perhaps the most personal of all the letters.  Titus, Luke, and Mark are all referenced.

Letter of Paul to Titus, meanwhile, is obviously another personal address to a notable colleague.  He's explaining why Titus was left in Crete, and how best to deal with the Cretans, which probably explains why we have that term today.  Which means in honor of this letter, if you hadn't been using it before, you should now (but in a loving way).

Letter of Paul to Philemon is the last one directly ascribed to Paul in the New Testament.  He's once again a prisoner as he's composing it.  Timothy is referenced.  He's basically directing matters from prison.  Mark and Luke are also referenced.