He became a clerical member of the Military Order of St. James, and accompanied the Bishop of Segovia to the Council of Trent (1562) where he won great distinction.

[1] On his return, he retired to a hermitage at Aracena whence he was summoned by King Philip II of Spain (1568) to supervise a new polyglot edition of the Bible, with the collaboration of many learned men.

Arias was responsible for a large part of the actual matter, besides the general superintendence, and in obedience to the command of the king took the work to Rome for the approbation of Pope Gregory XIII.

[1] León de Castro, professor of Semitic languages at Salamanca, to whose translation of the Vulgate Arias had opposed the original Hebrew text, denounced Arias to the Roman, and later to the Spanish Inquisition for having altered the Biblical text, making too liberal use of the rabbinical writings,[2] in disregard of the decree of the Council of Trent concerning the authenticity of the Vulgate, and confirming the Jews in their beliefs by his Chaldaic paraphrases.

He accepted, however, the post of a royal chaplain, but was only induced to leave his retirement for the purpose of superintending the Escorial library and of teaching Semitic languages.