Humbert of Romans, the master general of the order from 1254 to 1263, was a great administrator, as well as preacher and writer. It was under his tenure as master general that the sisters in the order were given official membership. Humbert was a great lover of languages, and encouraged linguistic studies among the Dominicans, primarily Arabic, because of the missionary work friars were pursuing amongst those led astray or forced to convert by Muslims in the Middle East. He also wanted his friars to reach excellence in their preaching, and this was his most lasting contribution to the order. The growth of the spirituality of young preachers was his first priority. He once cried to his students: "... consider how excellent this office [of preaching] is, because it is apostolic; how useful, because it is directly ordained for the salvation of souls; how perilous, because few have in them, or perform, what the office requires, for it is not without great danger ... , vol. xxv. (Lyon, 1677)