Being made a priest, at twenty-two, he was distinguished by the illustrious cardinal Borromeo with his confidence, and employed by him, on many occasions, not without the envy of persons of less merit, who were so far exasperated as to lay a charge against him, before the inquisition, for denying that the trinity could be proved from the first chapter of Genesis; but the accusation was too ridiculous to be taken notice of.
After this, he passed successively through the dignities of his order, and, in the intervals of his employment, applied himself to his studies with so extensive a capacity, as left no branch of knowledge untouched. By him Acquapendente, the great anatomist, confesses, that he was informed how vision is performed; and there are proofs, that he was not a stranger to the circulation of the blood.
He frequently conversed upon astronomy with mathematicians; upon anatomy with surgeons; upon medicine with physicians; and with chymists upon the analysis of metals, not as a superficial inquirer, but as a complete master.
But the hours of repose, that he employed so well, were interrupted by a new information in the inquisition, where a former acquaintance produced a letter, written by him, in ciphers, in which he said, "that he detested the court of Rome, and that no preferment was obtained there, but by dishonest means." This accusation, however dangerous, was passed over, on account of his great reputation, but made such impression on that court, that he was afterward denied a bishoprick by Clement the eighth. After these difficulties were surmounted, father Paul again retired to his solitude, where he appears, by some writings drawn up by him at that time, to have turned his attention more to improvements in piety than learning. Such was the care with which he read the scriptures, that, it being his custom to draw a line under any passage which he intended more nicely to consider, there was not a single word in his New Testament but was underlined; the same marks of attention appeared in his Old Testament, Psalter, and Breviary.
But the most active scene of his life began about the year 1615, when pope Paul the fifth, exasperated by some decrees of the senate of Venice, that interfered with the pretended rights of the church, laid the whole state under an interdict.
The senate, filled with indignation at this treatment, forbade the bishops to receive or publish the pope's bull; and, convening the rectors of the churches, commanded them to celebrate divine service in the accustomed manner, with which most of them readily complied; but the jesuits, and some others, refusing, were, by a solemn edict, expelled the state.
Both parties having proceeded to extremities, employed their ablest writers to defend their measures: on the pope's side, among others, cardinal Bellarmine entered the lists, and, with his confederate authors, defended the papal claims, with great scurrility of expression, and very sophistical reasonings, which were confuted by the Venetian apologists, in much more decent language, and with much greater solidity of argument.
On this occasion father Paul was most eminently distinguished, by his Defence of the Rights of the Supreme Magistrate; his treatise of Excommunications, translated from Gerson, with an Apology, and other writings, for which he was cited before the inquisition at Rome; but it may be easily imagined that he did not obey the summons.
The Venetian writers, whatever might be the abilities of their adversaries, were, at least, superiour to them in the justice of their cause. The propositions maintained on the side of Rome were these: that the pope is invested with all the authority of heaven and earth: that all princes are his vassals, and that he may annul their laws at pleasure: that kings may appeal to him, as he is temporal monarch of the whole earth: that he can discharge subjects from their oaths of allegiance, and make it their duty to take up arms against their sovereign: that he may depose kings without any fault committed by them, if the good of the church requires it: that the clergy are exempt from all tribute to kings, and are not accountable to them, even in cases of high treason: that the pope cannot err; that his decisions are to be received and obeyed on pain of sin, though all the world should judge them to be false; that the pope is God upon earth; that his sentence and that of God are the same; and that to call his power in question, is to call in question the power of God; maxims equally shocking, weak, pernicious, and absurd; which did not require the abilities or learning of father Paul, to demonstrate their falsehood, and destructive tendency.
It may be easily imagined, that such principles were quickly overthrown, and that no court, but that of Rome, thought it for its interest to favour them. The pope, therefore, finding his authors confuted, and his cause abandoned, was willing to conclude the affair by treaty, which, by the mediation of Henry the fourth of France, was accommodated upon terms very much to the honour of the Venetians.