Scholars argue over whether or not Paul's second letter to the Thessalonians was actually written by Paul or not, and the consensus leans in the direction of not. Certainly, II Thessalonians 1 opens the letter with a different "feel" from I Thessalonians, which is generally held to be an authentic Pauline epistle. It feels more judgmental of those who are not Christians and more bellicose for want of a better word. This different feel is seen esp. in verse 6, which reads in the NRSV, "For it is indeed just of God to repay with affliction those who afflict you," and in the Today's English Version (TEV), "God will do what is right: he will bring suffering on those who make you suffer." That is, the Christians in Thessalonica have suffered at the hands of others and God has every right to inflict suffering on those who have made the Christians suffer.
OK. One wonders, however, where this fits with the teachings of Paul himself, which are that we are to, "admonish the idlers, encourage the fainthearted, help the weak, be patient with all of them. See that none of you repays evil for evil, but always seek to do good to one another and to all." (I Thessalonians 5:14-15) Paul taught the Thessalonian faithful to be compassionate. Pseudo-Paul told them that God punished their persecutors by making them suffer. On the face of it, God doesn't play by the same rules as expected for followers of Jesus. They are to repay evil with good while God can repay evil with evil, that is suffering with suffering. They are to act with love while God acts with justice. The whole premise of the Christian faith is that God is merciful, slow to anger, loving, and forgiving.
On the face of it, II Thessalonians 1:6 contradicts the settled teachings of the actual Paul and the message so clearly delivered elsewhere in scripture.
Is possible, however, to resolve the contradiction between Paul and pseudo-Paul in at least one way. One of the fundamental spiritual laws planted deep within the human race is the law of karma, what goes around comes around. When we cause suffering we suffer. Now, it is of course not an ironclad law and often enough the agents of suffering cause more hurt than they suffer themselves. It is, nonetheless, true that agents of suffering often enough are as deeply hurt or more deeply hurt by the suffering they cause than are their victims. God created us this way, and by this spiritual law those who inflicted suffering on the Christians in Thessalonica did themselves suffer as well. God's karmic justice was done. Now, I seriously doubt that this interpretation of II Thessalonians 1:6 reflects the intention of the author. But in our time we can still discover the Word in the words. We are not constrained to read the words the way they were originally intended to be read 2,000 years ago so long as we read them in light of the person of Jesus Christ.