Even in Thessalonica you sent me help for my needs once and again. (ESV)
Ministry is difficult. If you are involved in some kind of ministry and you have not yet faced difficulty, you will. Sorry to be the bearer of bad news. The reality is that we are in a constant spiritual battle. The enemy is Satan himself, and he is not in favor of the Gospel being boldly preached. Thessalonica was a place where Paul ministered and found difficulty.
 Now when they had passed through Amphipolis and Apollonia, they came to Thessalonica, where there was a synagogue of the Jews.  And Paul went in, as was his custom, and on three Sabbath days he reasoned with them from the Scriptures,  explaining and proving that it was necessary for the Christ to suffer and to rise from the dead, and saying, “This Jesus, whom I proclaim to you, is the Christ.” (ESV)
The Apostle Paul had some success, but if you read further in Acts 17 you will find that some received his message, while others formed a mob against him. This ought not to surprise us at all. Jesus went all over Israel preaching the truth. He hung on a cross. Where there is truth proclaimed there are always consequences. Some are forgiven. Some are furious.
Paul's time in Thessalonica was short, yet stressful. The church at Philippi knew of Paul's situation and they took action. They sent help for him "once and again." Philippi is truly a model for all of us on how we should treat a minister in need. Yes, we should pray for him. Yes, we should be moved emotionally. But even more importantly, we should put our concern in action and give real help.
If you minister to someone I hope you will remain strong in the midst of difficulty. If you see someone struggling in the midst of ministry I pray that you will give them real help.