Summary: Examining the motivation for Paul's perseverance and service can encourage believers to persevere in the midst of a darkened world that increasingly opposes the Faith.
“I endure everything for the sake of the elect, that they also may obtain the salvation that is in Christ Jesus with eternal glory.” 
The Apostle has emphasised a concept that is not often welcomed today—hardship. Directing student ministries at a major pastoral school some years past, I often emphasised the need for the preacher boys to “pay their dues.” I daresay that the overwhelming majority of young men (and some not so young) who attended that school imagined that they would soon be pastoring megachurches. They knew they were great preachers, and it was only a matter of time until the saints recognised their superior abilities.
That the Apostle is continuing on the theme of hardship in service of the King becomes evident from the first word of the text—“Therefore!” When we read, we often give scant attention to prepositions such as the first word in this verse. However, he is drawing a logical conclusion from what he has just stated. In order to refresh our memories, look back to the opening verses of the letter. “You then, my child, be strengthened by the grace that is in Christ Jesus, and what you have heard from me in the presence of many witnesses entrust to faithful men who will be able to teach others also. Share in suffering as a good soldier of Christ Jesus. No soldier gets entangled in civilian pursuits, since his aim is to please the one who enlisted him. An athlete is not crowned unless he competes according to the rules. It is the hard-working farmer who ought to have the first share of the crops. Think over what I say, for the Lord will give you understanding in everything.
“Remember Jesus Christ, risen from the dead, the offspring of David, as preached in my gospel, for which I am suffering, bound with chains as a criminal. But the word of God is not bound” [2 TIMOTHY 2:1-9]!
Paul has enjoined the pastor especially to prepare men for ministry, equipping them to serve. Fulfilling this responsibility will entail suffering; but suffering because of service to the Master is to be embraced, not spurned. Suffering itself is not particularly praise-worthy; suffering because of the Faith merits the Saviour’s commendation. We have Jesus’ statement on this matter. “Blessed are those who are persecuted for righteousness’ sake, for theirs is the kingdom of heaven.
“Blessed are you when others revile you and persecute you and utter all kinds of evil against you falsely on my account. Rejoice and be glad, for your reward is great in heaven, for so they persecuted the prophets who were before you” [MATTHEW 5:10-12]. Mark well that the anticipated reward is “in heaven.” That reward is not, as many imagine, given at this time.
Throughout the preceding verses, Paul has insisted that the pastor must have the singular focus of fulfilling the appointment received from the Lord of Glory. The soldier aims to please the one who enlisted him. The athlete must compete according to the rules. The farmer must toil if he anticipates a share of the crop. However, in each instance success is recognised and rewarded only at the completion of the battle, or after the contest is concluded, or after the crop is harvested. Until the appointment is fulfilled, all must anticipate toil, deprivation and exhausting labour. Just so, in pastoral service, no man should expect praise and commendation.