An expression may be difficult for a beginner and immediately clear to a trained scholar. Similarly, customary idioms familiar to an early audience may require explanation centuries later. Thus difficulty in understanding is partly relative to the reader.
Knowing a dictionary translation is not identical to recognizing all argumentative functions and contextual implications. The degree of explanation can vary with an audience’s training without changing the text’s established sense.
Example: an Arabic idiom familiar to early speakers may need explanation for a modern learner. Explaining it recovers an established usage; it does not create a new meaning.