The esteemed Oxford professor Sir Diarmaid MacCulloch follows his comprehensive Christianity: The First Three Thousand Years with a briefer but no less eloquent study of Silence: A Christian History (Viking, $27.95). When part of the devotional continuum taking a soul from active meditation (often aided by silent icons) to the purer state of contemplation, silence has been a virtue and a blessing. It’s also been a shield, used by 16th-century conversos who practiced Christianity but maintained an unspoken devotion to Judaism or Islam. But silence can hide what ought to be revealed, and in this it’s been a sin of both omission and commission, whether as the Catholic Index of banned books or the concealment of child abuse, or the wider Christian tacit approval of slavery, which isn’t explicitly condemned in the New Testament. And what about that term, New Testament, anyway? MacCulloch points out that it turned Hebrew scripture into “the Old Testament,” silencing its identity as the Tanakh and making it merely a prelude to the Christian gospels. Deeply researched, this book yields many such telling details; for instance, the silence most widely practiced now, the public moment in remembrance of the dead, started in 1912, after the Titanic disaster.