At least, that's what I hear when I read this second letter he writes to young Timothy, his son in the faith.
There's a sort of passing-the-baton going on here, with Paul giving advice to Timothy, and warning him about what and who to watch out for. There's a little world-weariness (everyone who wants to live a holy life is going to be harassed, Paul says). There is some sadness, as Paul lists off people who have deserted either him or the faith, or both.
Getting old is not for sissies.
Usually, when I say this I mean it's because of health issues, or because people who get old have to watch their friends die. But in this case, Paul is getting older, and looking back and even though he can look back to all of the good things he's done, and his accomplishments, he also gets to look back and see the things that are not going well right now, too. He sees those who used to be fervent in the faith, and now have cooled off. He sees people who were well-thought-of, but now have gone astray. He gets the long view.
But there's a lot of wisdom in these short chapters, too. There's a little bit of "rule-keeping" exhortation (like people in the military, or athletes, you will benefit by following the rules, he says.) But I think he's talking not so much about "rule-following" for it's own sake (which is about as far from Paul's theology as I can imagine) but about practice. Athletes practice; military people practice. You too will benefit by the discipline of practicing your faith.
One of the most famous passages about scripture is in this letter, "All Scripture is inspired by God and is useful for teaching, for exhortation....." what I like about this passages is that scripture is useful, but not always in the same way: God does different things in us through our hearing of Scripture: teaching exhortation, comfort, encouragement..... I think that the least helpful way we can think of Scripture is as a map or a guide (those "owner's manual's you get for cars? who cracks open those books, except when you are in trouble?). Let's revel in the surplus of meaning in scripture, not just keep it in the glove compartment of our cars for when we break down.
Finally, Paul passage the baton when he says to Timothy, "I have fought the good fight." In his last letter, he exhorts, "Fight!" Now he looks back and says, "I have fought the good fight. I have finished the race." The crown of righteousness refers to the laurel wreath reserved for the winners in athletic tournaments. Paul has already won because he already belongs to Christ, even though many people have deserted him, even though he is lonely, even though he needs his friends to come to me.
The letter ends with all sorts of small personal details: come and visit, bring my coat, also bring the scrolls and parchments. Bring Mark. No one is with me, except Luke. No one took my side in the court hearing. Greet Prisca and Aquila.