A student who has memorized a surah needs daily revision of previous portions while learning new passages. New memorization may grow while older sections weaken if they are not revisited with care.
Example 1: The student learns today’s verses and then recites yesterday’s passage without looking.
Example 2: When a mistake occurs, the surrounding phrase is reviewed, not just the isolated word.
The imperative تَعَاهَدُوا carries a sense of ongoing care. One unusually long session is not always a substitute for consistent, manageable review.