When a word or phrase is kept in the mind for a certain length of time, without being mixed with other ingredients, it seems to infiltrate every part of the brain ... At our ordinary reading speed no such infiltration normally occurs. But it does sometimes happen when you read the work of a poet you particularly admire, or read the Bible, dwelling on every word and taking ample time over it. On such an occasion you may be reading word by word, carefully and with deep appreciation, and suddenly the passage will seem charged with infinite meaning, seeming almost to come as a revelation from heaven. Anyone who has ever read the Bible with devoted piety must have had such an experience. We call this sort of reading "[language samadhi,"] and it is this that we must achieve when reciting a Zen koan.
Katsuki Sekida, Zen Training, p99