In theology Collier was an adherent of the High Church party, though his views were by no means orthodox. In the Jacobite Mists Journal he attacked Bishop Hoadly's defence of sincere errors. His views on the problems of Arianism, and his attempt to reconcile it with orthodox theology, are contained in "A Specimen of True Philosophy" (1730, reprinted in Metaphysical Tracts, 1837) and "Logology, or a Treatise on the Logos in Seven Sermons on John 1. 1, 2, 3, 14" (1732, analysed in Metaph. Tracts). These may be compared with Berkeley's "Sins".