We should always interpret and apply individual portions of Scripture in light of the immediate context - the Scripture surrounding them - and in light of the overall revelation of Scripture. "The whole counsel of God," it has often been called. Otherwise we can miss some of the deeper truths.
Consider Jesus Christ's famous "Sermon on the Mount" in chapter 5 of Matthew's Gospel, specifically [5:43-48]. Jesus' instructions are hard to misunderstand in their immediate context. By and large, I think few people do. "You have heard that it was said, 'You shall love your neighbor and hate your enemy.' But I say to you, love your enemies, bless those who curse you, do good to those who hate you, and pray for those who spitefully use you and persecute you, that you may be sons of your Father in heaven; for He makes his sun rise on the evil and on the good, and sends rain on the just and on the unjust."
However, like many things Jesus said, this has more than one dimension to it. In His own later prophecy in Matthew chapter 25, concerning His giving of judgment at the end of human history, He made clear that He identifies personally with His children and with how each of us has been treated. Both to the righteous, (in a positive sense), and the condemned, (negatively), Jesus says he will tell everyone that what they did or failed to do to "one of the least of these my brethren," [verse 40 and verse 45], they did or failed to do to Him.
In his second letter to Thessalonica, the Apostle Paul minced no words. The Christian church in that city was undergoing harassment and persecution by its enemies. Some of the Christians and those persecuting them had once been members of the same synagogue, (see Acts 17). When Paul first reasoned with the Thessalonian Jews from the Scriptures, some of them believed in Jesus as Messiah. They were followed by "a great multitude of the devout Greeks, and not a few of the leading women," (verse 4). Unfortunately, this made the rest of the synagogue envious. Until then, these "devout Greeks" were those who had been following them. This short little homely guy, Paul, showed up and after only three weeks they were following him instead. The persecution that began then probably continued after Paul's new Christian friends sent him away by night.
Second Thessalonians is a short letter. It is three chapters long and in my New Testament it only covers about 2-2/3 pages. By the third sentence, Paul is already telling them, "...Since it is a righteous thing with God to repay with tribulation those who trouble you." (v.6). He speaks of Christ appearing from heaven with his "mighty angels", (chubby childlike cherubs were a medieval European invention), "in flaming fire taking vengeance on those who do not know God, and on those who do not obey the gospel of our Lord Jesus Christ." (v.8). Yet, Peter said in his second epistle, (II Peter 3:9), "The Lord is not slack concerning His promise, as some count slackness, but is longsuffering toward us, not willing that any should perish but that all should come to repentance."
Putting this all together, we come back to the thought expressed in the title of this post. By all means, we are supposed to be concerned for the salvation of the lost - if we can bring ourselves to be so politically incorrect as to call them "lost" - and when persecuted we are supposed to pray for them. If we are truly saved, we appreciate that it is by the grace of God that we have come to believe and appreciate the truth of the Scriptures and the perfect character of God and His Son, Jesus Christ. In the end, I believe one reason God has inspired these things to be written in Scripture is to make us realize how much our lost co-workers, neighbors, friends or relatives need our prayers. Eventually, either they will go to Him or He will come to Earth and then - just like some of us who are parents, who would have to restrain ourselves from rending to pieces anyone who would harm our child - He will take personally what has been done to us.
I hope that it will sound much less flippant now when I say, "Pray for your enemies - they'll need it."
(See "About Me")