Before a year had passed Fletcher's health began to fail, and he was glad to devote himself to the writing which proved so useful and convincing. To Mr. Ireland he wrote:-- "My throat is not formed for the labours of preaching. When I have preached three or four times together it inflames and fills up; and the efforts which I am then obliged to make heat my blood. Thus I am, by nature, as well as by the circumstances I am in, obliged to employ my time in writing a little. O that I may be enabled to do it to the glory of God!" Perhaps nothing he wrote more fully conduced to that lofty purpose than his famous "Polemical Essay on the Twin Doctrines of Christian Imperfection and a Death Purgatory"; than which few clearer, more convincing, or more able vindications of Scriptural holiness have ever been written. Can aught be plainer than the definition of Christian perfection which follows:-- "...Christian perfection is nothing but the depth of evangelical repentance, the full assurance of faith, and the pure love of God and man shed abroad in a faithful believer's heart, by the Holy Ghost given unto him, to cleanse him, and to keep him clean, 'from all filthiness of the flesh and spirit'; and to enable him to fulfil the law of Christ' according to the talents he is entrusted with, and the circumstances in which he is placed in this world.... This is evident from the descriptions of Christian perfection which we find in the New Testament." In a practical, almost homely, manner, Fletcher deals with questions we often hear put to-day. For instance :-- "_How many baptisms, or effusions of the sanctifying Spirit, are necessary to cleanse a believer from all sin, and to kindle his soul into perfect love?..._ If you asked your physician how many doses of physic you must take before all the crudities of your stomach can be carried off, and your appetite perfectly restored, he would probably answer you that this depends upon the nature of those crudities, the strength of the medicine, and the manner in which your constitution will allow it to operate, and that, in general, you must repeat the dose, as you can bear, till the remedy has fully answered the desired end. I return a similar answer: If one powerful baptism of the Spirit 'seals you unto the day of redemption,' and 'cleanses you from all' moral 'filthiness,' so much the better. If two or more are necessary, the Lord can repeat them.