وَقَدْ كَانَ مِنْهُ الْبَرُّ وَالْبَحْرُ مُتْرَعَا
Yet land and sea alike were, as it were, overflowing from his generosity.
The mention of land and sea gives the man's generosity an expansive image. The description “overflowing” expresses abundance rather than a literal physical condition.
Taken together with the question addressed to the grave, the image makes the grief over Maʿn more intense. The rhetorical purpose is lament and pain, not obtaining an answer from the grave.