‘Venerable Nāgasena, those two qualities of black iron you say he ought to take, which are they?’
‘Just, O king, as black iron even when beaten out carries weight; just so, O king, should the mind of the strenuous Bhikshu, earnest in effort, be able, by his habit of thoughtfulness, to carry heavy burdens. This, O king, is the first quality of black iron he ought to have.
‘And again, O king, as black iron does not vomit up the water it has once soaked in ; just so, O king, should the strenuous Bhikshu, earnest in effort, never give up the faith he has once felt in the greatness of the Blessed One, the Supreme Buddha, in the perfection of his Doctrine, in the excellence of the Order—never give up the knowledge he has once acquired of the impermanence of forms, or of sensations, or of ideas, or of qualities, or of modes of consciousness. This, O king, is the second quality of black iron he ought to have. For it was said, O king, by the Blessed One, the god over all gods:
“That man who is in insight purified,
Trained in the doctrine of the Noble Ones,
Grasping distinctions as they really are,
What need hath he to tremble? Not in part
Only, but in its full extent, shall he
To the clear heights of Arahatship attain.”’