The opening pages of the Reasonableness straightforwardly opposed original sin. Locke declared it ‘obvious to any one, who reads the New Testament, that the doctrine of redemption … is founded upon the supposition of Adam's fall’. It was therefore necessary to consider what was lost by Adam in order to discover what Christ had restored to men. Locke declared that identifying Adam's loss required a ‘diligent and unbiassed search’ of Scripture because the ‘two extremes, that men run into on this point, either on the one hand shook the foundations of all religion, or, on the other, made Christianity almost nothing’. Some ‘would have all Adam's posterity doomed to eternal infinite punishment, for the transgression of Adam, whom millions had never heard of, and no one had authorised to transact for him, or be his representative’. Others – surely Deists such as Acosta – had found this inconsistent with ‘the justice or goodness of the great and infinite God’ and so had ‘thought that there was no redemption necessary’, making Jesus Christ ‘nothing but the restorer and preacher of pure natural religion’. Locke condemned these last interpreters of doing ‘violence to the whole tenour of the New Testament’.

For Locke, it was ‘visible’ to the ‘unbiassed’ that what Adam had lost was ‘bliss and immortality’. The declaration of 1 Cor. 15:22 that ‘in Adam all die’ was interpreted by some as ‘a state of guilt, wherein not only he, but all his posterity was so involved, that every one descended of him deserved endless torment, in hell fire’.