About 1611, the year in which he commenced MA, he heard a sermon at St Mary's from
John Cotton, then fellow of
Emmanuel, which opened to him a new career. Cotton had a great reputation as an elegant preacher; but this was a plain evangelical sermon, and disappointed his audience. He returned to his rooms, somewhat mortified by his reception, when Preston knocked at his door, and that close religious friendship began which permanently influenced the lives of both. Preston now gave himself to the study of scholastic divinity;
Aquinas seems to have been his favourite ; he thoroughly mastered also
Duns Scotus and
William of Ockham. His biographer tells a curious story of his activity in securing the election (1614) of
John Davenant as master of Queens' in succession to Tyndal.
George Montaigne, afterwards
Archbishop of York, had his eye on this preferment; but immediately on Tyndal's death Preston rode post-haste to London, reaching
Whitehall before day-break. Here he made interest with
Robert Carr, 1st Earl of Somerset, with a view to secure court sanction for the choice of Davenant. Returning to Cambridge, he had the election over before Montaigne got wind of the vacancy. During the visit of
James I to Cambridge in March 1615, Preston distinguished himself as a disputant. He was chosen by
Samuel Harsnett, the vice-chancellor, as 'answerer' in the philosophy act, but this place was successfully claimed by
Matthew Wren, and Preston took the post of first opponent. His biographer,
Thomas Ball, gives an account of the disputation on the question 'Whether dogs could make
syllogismes'. Preston maintained that they could. James was delighted with his argument (which Granger thinks Preston borrowed from a well-known passage in Montaigne's
Essays), and introduced a dog story of his own. 'It was easy to discerne that ye kings hound had opened a way for Mr. Preston at ye court'.
Sir Fulke Greville, 1st Baron Brooke, became his firm friend (he ultimately settled £50 a year upon him). But Preston had by this time given up his early ambition; though he said little of his purpose, his mind was set on the ministry, and he was reading modern divinity, especially
Calvin. ==Puritan leanings==