Two men of mark in English Literature, Southey and Alexander Smith, have called Cowper "the best of English letter-writers," and few will be found to challenge this opinion.
The charm of Cowper's letters, like that of his poetry, lies first of all in his naturalness and sincerity. He writes simply because he has something to say, or because he loves his correspondent, and has no idea of posing for effect. He never dreamt of his letters being published when he wrote them. It was so with his first poems. He wrote to drive away melancholy, or to amuse his friends, and carelessly sent the last piece written to whatever friend he happened to be addressing, and was nearly fifty years old before the idea of publishing any of these pieces was suggested to him.
His letters, then, are the simple statement of whatever he has in his mind; written in pure and beautiful English; full of the information and refined taste of a well-read man; overflowing now with humour, now with deep religious feeling, for both were natural to him. It follows, as a matter of course, that they are deeply interesting as materials for the biography of the poet, though here one caution is needed.