By this point, Foster was starting to publish controversial works on Christian doctrine. His
Essay on Fundamentals showed the influence of
Samuel Clarke's
Scripture Doctrine, the work which had triggered the Exeter Controversy, and which Hallett's students, most notably Stogdon, had encountered and read secretly several years earlier. Like Clarke, Foster hinted at the non-essentiality of the doctrine of the Trinity; he argued that the fundamentals of the Christian faith should operate in a marriage between reasonable interpretation of natural and revealed religion. He also came to denounce infant baptism after reading
John Gale's antipaedobaptist tracts; he believed it not to be sanctioned by scripture doctrine, and offered himself up to be re-baptized as an adult believer in London, perhaps by Gale himself. From 1724 Foster took over from Gale as co-minister with Joseph Burroughs at the General Baptist chapel in Paul's Alley, Barbican, London. By this point his Socinian leanings were well known; he and Burroughs were the only London ministers to invite the disgraced and formerly imprisoned Arian heretic
Thomas Emlyn to preach. From 1728 Foster supplemented his ministry with the newly established Sunday evening lecture at the
Old Jewry. By 1744 he succeeded
Jeremiah Hunt as pastor of the Independent congregation at Pinner's Hall. Emlyn was not the only radical with which he had known sympathies. The rebellious
Earl of Kilmarnock declared himself a presbyterian, and was given the sacrament whilst he was imprisoned in the
Tower of London by Foster, who also attended his execution. Foster published an
Account of Kilmarnock's behaviour in 1746, after which he was viciously attacked for
Jacobitism, a claim which was far from the truth. Under the pressure of the sustained criticisms, his health began to fail. == Support for Foster ==