What were the pivotal doctrinal points for John Biddle and the English Unitarians? This research deserves to be taken further to understand the meshing of beliefs and ideals that forged links between the Polish Brethren and the English Unitarians during the 17th century. The defense of the Trinity was assimilated into the panorama of the English political-theological debate from the first half of the 17th century, along with the contribution of the translators and editors of the works of the Church Fathers to the construction of the theological and doctrinal identity of the English Church. Conversely, in the conviction of remaining within Protestant biblical hermeneutics, the Antitrinitarian creed stressed the unity and oneness of God expounded in Holy Scripture while intending to demonstrate that the trinitarian interpretations of the Catholics were paradoxical. Biddle’s works of theology and doctrinal polemic in particular, and his work as a translator, can help to clarify these affinities and differences and open new paths of research into his influence in the time of Locke and on Locke’s own thought.