Locke agrees with Augustine and Aquinas that miracles can contribute to the reasonableness of Christianity. So miracles may give believers their principal ground for holding that the teaching of Christ is from God and that Jesus is the Messiah. Nevertheless he also affirms that there are other factors which properly have a bearing on the rational exercise of faith. So, for Locke, what purports to be revealed truth can be subjected to at least a negative test: if it conflicts with any of our intuitive knowledge, then it cannot be revealed by the ‘Author of our being’ because if such a proposition were to be true, this fact would ‘overturn all the principles and foundations of knowledge he has given us’. Locke goes on to widen the appeal, so that genuine revelation cannot conflict with anything which is established by the principles of knowledge which he has set forth in the Essay Concerning Human Understanding. Yet how, positively, may we recognise a revelation for what it is, from among the claimed revelations which do not actually contradict the deliverances of rational enquiry?

Locke answers that the fulfilment of prophecy and the working of miracles are the principal outward signs by which the true revelation is to be recognised. In relation to the latter he says ‘The evidence of our Saviour's mission from heaven is so great, in the multitude of miracles he did, before all sorts of people, that what he delivered cannot but be received as the oracles of God and unquestionable verity’.