“He prayeth best, who loveth best All things both great and small;”
The Mariner’s concluding moral links genuine prayer with love extending beyond human beings to the wider created world.
Source details
The Rime of the Ancient Mariner, Part VII, Project Gutenberg #151. ‘He prayeth best, who loveth best / All things both great and small’ belongs to the Mariner's explicitly Christian concluding lesson after his supernatural ordeal, immediately following the parallel line about loving ‘Both man and bird and beast.’ It is fictional poetic speech and religious-moral language, not a neutral scientific, theological or animal-behavior proposition.