was published in Latin at Amsterdam in 1676, and was an elaborate statement of the grounds for holding certain fundamental positions laid down in the Theses. It was translated by its author into English in 1678, and is claimed to be "one of the most impressive theological writings of the century".

The Apology, however, failed to arrest the persecution to which the Quakers were exposed, and Barclay himself, on returning from Europe, where he travelled extensively (once with