Walter Marshall, from The Gospel Mystery of Sanctification:
Experience shows plentifully, both of heathens and Christians, how pernicious ignorance, or mistaking of those effectual means, is to a holy practice. The heathens generally fell short of an acceptable performance of those duties of the law which they knew, because of their ignorance in this point:
(i) Many Christians content themselves with external performances, because they never knew how they might attain to spiritual service.
(ii) And many reject the way of holiness as austere and unpleasant, because they did not know how to cut off a right hand, or pluck out a right eye, without intolerable pain; whereas they would find ‘the ways of wisdom’ (if they knew them) ‘to be ways of pleasantness, and all her paths to be peace’ (Prov. 3:17). This occasions the putting off repentance from time to time, as an uncouth thing.
(iii) Many others set on the practice of holiness with a fervent zeal, and run very fast; but do not tread a step in the right way; and, finding themselves frequently disappointed and overcome by their lusts, they at last give over the work and turn to wallow again in the mire – which has occasioned several treatises, to show how far a reprobate may go in the way of religion, by which many weak saints are discouraged, accounting that these reprobates have gone farther than themselves; whereas most of them never knew the right way, nor trod one step right in it, for, ‘there are few that find it’ (Matt. 7:14).
(iv) Some of the more ignorant zealots do inhumanly macerate their bodies with fasting and other austerities, to kill their lusts; and, when they see their lusts are still too hard for them, they fall into despair and are driven, by horror of conscience, to make away with themselves wickedly, to the scandal of religion.