What you have before you, for the first time in English, is a reformational jewel by the Spanish reformer Cipriano de Valera. In his Treatise, originally written for those protestant believers enslaved by the Barbary pirates, or corsairs, Valera masterfully comforts, exhorts, and edifies, while providing a deconstruction of Roman Catholicism, Judaism, and Islam. Perhaps most remarkable is his encouragement to those faithful held captive to witness to their captors, in both speech and life action, harbouring deep within a hope that the seed of the gospel planted by the captives would produce life-transforming fruit in their captors. Valera had the audacity to believe, as we all should, that the gospel can transform the hearts of those whom we might perceive as our most bitter enemies. That should provoke us to equal or greater faith in what the gospel can accomplish by the power of the Spirit of God.