[1][3][5] Fausto Sozzini recollected most of his uncle Lelio's religious writings by traveling over again his routes throughout early modern Europe, and systematized his Antitrinitarian beliefs into a coherent theological doctrine.

[1] His polemical treatise De sacrae Scripturae auctoritate (written in the years 1580s and published in England in 1732, with the title A demonstration of the truth of the Christian religion, from the Latin of Socinius) was highly influential on Remonstrant thinkers such as Simon Episcopius, who drew on Sozzini's arguments for viewing the sacred scriptures as historical texts.

To the able women of his family he owed the strong moral impress which marked him through life; his early intellectual stimulus came from his uncle Celso Sozzini, a nominal Catholic, but an esprit fort, founder of the short-lived Accademia del Sizienti (1554), of which young Fausto was a member.

[7] Coming of age (1561) he went to Lyon, probably engaging in mercantile business; he revisited Italy after his uncle Lelio Sozzini's death; we find him in 1562 on the roll of the Italian church at Geneva; there is no trace of any relations with Calvin.

Francesco was doubtless aware of the motive which led Sozzini to quit Italy; there is every reason to believe Samuel Przypkowski's statement that the grand-duke agreed to secure to him the income of his property so long as he published nothing in his own name.

[7] Sozzini now fixed himself at Basel, gave himself to close study of the Bible, began translating the Psalms into Italian verse, and, in spite of increasing deafness, became a centre of theological debates.

His discussion with Jacques Couet on the doctrine of salvation issued in a treatise De Jesu Christo servatore (finished 12 July 1578), the circulation of which in manuscript commended him to the notice of Giorgio Biandrata, court physician in Poland and Transylvania, and ecclesiastical wire puller in the interests of heterodoxy.

The current existing ruler, Christopher Bathory, favoured the Jesuits; it was now Biandrata's object to limit the Judaic tendencies of the eloquent anti-Trinitarian bishop, Ferenc Dávid (1510–1579), with whom he had previously co-operated.

He was willing that Dávid should be prohibited from preaching pending the decision of a general synod; and his references to the case show that (as in the later instances of Jacobus Palaeologus, Christian Franken and Martin Seidel) theological aversions, though they never made him uncivil, froze up his native kindness and blinded his perceptions of character.

[13] Biandrata ultimately conformed to the Catholic Church; hence Sozzini's laudatory dedication to him (1584) of his De Jesu Christi natura, in reply to the Calvinist Andrew Wolan, though printed in his works, was not used.

He was asked by the Polish Brethren to take up the position of a champion of conscientious objection against the Belarusian Symon Budny and the Greek Unitarian Jacobus Palaeologus after Gregory Pauli of Brzeziny had become indisposed, and thereby gained some respect among the Poles.

[citation needed] Fausto Sozzini converted the Arian section of the Ecclesia Minor from belief in the pre-existence of Christ to the early Unitarian position, and from their rejection of the invocatio Christi.

They include all Sozzini's extant theological writings, except his essay on predestination (in which he denies that God foresees the actions of free agents) prefixed to Castellio's Dialogi IV (1575, reprinted 1613) and his revision of a school manual Instrumentum doctrinarum aristotelium (1586).

The former was first published (Seville [London, John Wolfe], 1588) by López, a Jesuit, who claimed it as his own, but prefixed a preface maintaining (contrary to a fundamental position of Sozzini) that man by nature has a knowledge of God.

In small compass it anticipates the historical argument of the credibility writers; in trying it by modern tests, it should be remembered that Sozzini, regarding it (1581) as not adequately meeting the cardinal difficulties attending the proof of the Christian religion, began to reconstruct its positions in his Lectiones sacrae (unfinished).