Innocent thoughts become sinful
Hence even those thoughts which are occasioned by weakness or disease, by the natural mechanism of the body, or by the laws of vital union, however innocent they may be in themselves, do nevertheless become sinful when they either produce or cherish and increase in us any sinful temper: suppose the desire of the flesh, the desire of the eye, or the pride of life (1 John 2:16). In like manner the wandering thoughts which are occasioned by the words or actions of other men, if they cause or feed any wrong disposition, then commence sinful. And the same we may observe of those which are suggested or injected by the devil. When they minister to any earthly or devilish temper (which they do whenever we give place to them, Ephesians 4:27, and thereby make them our own), then they are equally sinful with the tempers to which they minister.
1771 text
4. Hence even those thoughts which are occasioned by weakness or disease, by the natural mechanism of the body, or by the laws of vital union, however innocent they may be in themselves, do nevertheless become sinful, when they either produce or cherish and increase in us any sinful temper: suppose the desire of the flesh, the desire of the eye, or the pride of life. In like manner the wandering thoughts which are occasioned, by the words or actions of other men, if they cause or feed any wrong disposition, then commence sinful. And the same we may observe of those which are suggested or injected by the devil. When they minister to any earthly or devilish temper (which they do, whenever we give place to them, and thereby make them our own) then they are equally sinful, with the tempers to which they minister.