In 1854 he was ordained to a curacy at Bagnelstown, County Carlow, and on taking up his residence there began to show very great interest in the work of the London Society for promoting Christianity among the Jews.
The question of Jewish conversion was at that time agitating the religious world in England, and Barclay supported the cause in his own neighbourhood with great activity, till in 1858 he offered himself to the London Society as a missionary.
[1] In 1861 he was nominated incumbent of Christ Church, Jerusalem, a position requiring energy and tact to avoid entanglement in the quarrels of the parties whose rivalries Barclay describes as a ‘fretting leprosy’ neutralising his best efforts.
This was in 1870; he returned again to England and filled for a time the curacies of Howe, Lincolnshire and St. Margaret's, Westminster, till in 1873 he was presented to the living of Stapleford in the St. Albans diocese.
He preached in Spanish, French, and German; he was intimately acquainted with Biblical, Mishnaic Hebrew and Judaeo-Spanish, the dialect spoken by the Sephardic Jews.