Brainerd 9

I doubt not but that all who have well observed mankind will readily grant this, that it is not all those who by their natural constitution or temper are most disposed to dejection, that are the persons who are the most susceptive of lively and strong impressions on their imagination, or the most subject to those vehement impetuous affections, which are the fruits of such impressions; 

but that many who are of a very gay and sanguine natural temper are vastly more so, and if their affections are turned into a religious channel, are much more exposed to enthusiasm than many of the former. 

And as to Mr. Brainerd in particular, notwithstanding his inclination to despondency, he was evidently one of that sort of persons who usually are the furthest from a teeming imagination; 

being one of a penetrating genius, of clear thought, of close reasoning, and a very exact judgment and knowledge of things in divinity, but especially in things appertaining to inward experimental religion; 

most accurately distinguishing between real solid piety and enthusiasm, between those affections that are rational and scriptural, having their foundation in light and judgment, and those that are founded in whimsical conceits, strong impressions on the imagination, and those vehement emotions of the animal spirits that arise from them.