WE'VE all had appointments. Appointments are specific events at specific places with specific people and for specific purposes. And, I'm sure we've all had someone else set up an appointment for us a time or two. But I can't recall ever accepting an appointment "to be in pain" (at least, not for that purpose exclusively). I can think of a few medical appointments that I expected to include some pain. So, some appointments are less exciting than others. But in life, God has appointed us to certain & specific afflictions (John 16:33). Of course, Paul is the most perfect example of this. Jesus told Ananias that Paul had been chosen to endure much suffering for the glory of God and for the purpose of the propagation of the gospel (Act 9:16). As he proceeded, Paul knew pain was coming, but he proceeded anyway.
Like Jesus (Matthew 10:34), Paul didn't try to hide the coming of afflictions from those to whom he preached the gospel. There is indeed a place for calling potential converts to take up their cross & follow Christ. Here in chapter 3, verse 3 we find that the believers in Thessalonica certainly knew that pain was in their future. Paul had told them that they would suffer (vs. 4). But, seeing that God is good & loving, it is not surprising that, with their affliction, God also prepared comfort (vs. 2). This is His way. He allows us to be tempted, but He also provides for us help in times of need (vs. 13). Of course, we have to reach out & accept those helps.