[1][2] He was seen in his own time and by Edmund Venables in the Dictionary of National Biography to have been a trimmer (conforming politically for advancement's sake), and have a reputation mixed with his academic and other writings on casuistry.
Barlow was a learned Calvinist, who opposed Jeremy Taylor and George Bull, and with Thomas Tully was one of the guardians in Interregnum Oxford of acceptable orthodoxy.
[4] Barlow wrote at the request of Robert Boyle an elaborate treatise on "Toleration in Matters of Religion" at this time, but it was not published until after his death (in Cases of Conscience, 1692).
[7] On the other hand, Barlow was one of a group of Oxford grandees hostile to the Royal Society, along with John Fell, Obadiah Walker, and Thomas Pierce.
[8] He was an enemy of the "new philosophy" (as propounded by leading Royal Society members), giving as his confessional reasons that it was "impious if not plainly atheistic, set on foot and carried on by the arts of Rome," so designing to ruin the Protestant faith by disabling men from defending the truth.
[4] As pro-vice-chancellor of the university in 1673, he called in question William Richards, Chaplain of All Souls College, for Arminian doctrine in a sermon at St Mary's.
[3][4] In 1675, Barlow became Bishop of Lincoln through the good offices of two secretaries of state, Sir Joseph Williamson and Henry Coventry, both graduates of Queen's College, the latter having been his pupil; Gilbert Sheldon was opposed.
The Bishop's Palace at Lincoln had still not been repaired after the damage done in the English Civil War, although George Savile, 1st Marquess of Halifax remonstrated with Barlow on the subject in 1684.
In 1678, when Titus Oates forwarded his theory of a Popish Plot, Barlow had publicly declared enmity to the papists and their supposed leader, James, Duke of York.
When the bill enforcing a test against popery was introduced, which excluded such peers from the House of Lords, Gunning of Ely defended the church of Rome from the charge of idolatry, but Barlow answered him vehemently.
In 1680, while the Popish Plot panic was still at its height, he republished under the title of Brutum Fulmen, the papal bulls of Pius V and Paul III, pronouncing the excommunication and deposition of Queen Elizabeth and of Henry VIII, with inflammatory comments, and learned proofs that "the pope is the great Antichrist, the man of sin, and the son of perdition."
"[4] When in 1684 Henry Viscount St John was convicted of killing Sir William Estcourt in a brawl,[11] and Charles II used the royal prerogative for his pardon, Bishop Barlow published an elaborate tract (1684–1685) in support of regal power to dispense with penal laws.
This was succeeded by "a case of conscience", proving that kings and supreme powers had authority to dispense with the positive precept condemning murderers to death.
[17] Many of the printed books in Barlow's library that are currently held at the Bodleian reflect his interest in theology, the reign of Charles I, and events during the English Civil War and Interregnum.
These include many shorter polemical pamphlets and tracts related to volatility in the 1640s and 50s such as Barlow's manuscripts at the Bodleian cover a range of subjects, genres, and time periods.