We rejoice in our sufferings.
Paul shows what true Christian boasting is, namely, to boast, rejoice, and be proud in suffering, shame, weakness, etc. The world not only regards Christians as the most despicable of men; but with vehemence and what it regards as righteous zeal it hates, persecutes, condemns, and kills them as a dangerous menace to both the spiritual and the earthly realm, in other words, as heretics and revolutionaries. But because they are not suffering on account of murder, stealing, and other such crimes, but on account of Christ, whose blessings and glory they proclaim, they glory in their afflictions and in the cross of Christ. With the apostles they "rejoice that they are counted worthy to suffer dishonor for the name of Christ" (Acts 5:41).
From Lectures on Galatians (1535) (Luther's Works 27:133)