Paul sent Timothy to check on the Thessalonians, to strengthen them in the midst of their persecution. He reminds them that they should expect suffering because of their faith in Christ. It should never surprise them, or worse yet, cause them to buckle and stop living a life of faith. His hope is to see all believers endure until death or until Christ’s return without abandoning their faith; if they are tempted by Satan to give into suffering and quit Christ, then Paul’s work as an apostle will have been wasted. He does not want to simply get people into Heaven; he wants believers to fully mature in their lives and walk the path Christ has set before them, which involves suffering like Christ did.
Timothy reported to Paul that the Thessalonians were thriving despite their persecution. They continue in faith and love, and they miss Paul as much as he misses them. He is comforted by this news, and declares that when believers overcome suffering, we are living out the fullest, most rewarding life God intended for us. It restores life into Paul to learn that the Thessalonians are doing well despite their challenges.
Although they are enduring, Paul still desires to see them in person and to teach them more. He tells them to love each other and all other people with an overflowing love. Love is the means by which Jesus prepares us for His return to earth, so that He will find us living a life set apart from the world which He will judge.