In Mark 10:21, in the spiritual sense selling can be understood as rejecting the falsities which were the doctrine of the Jewish nation, and receiving the doctrine of truth from the Lord.

'To sell,' as in Revelation 8:17, signifies teaching doctrine.

'To sell,' as in Genesis 41:56, means transferring to another as their own, because what is sold becomes the property of the one who buys it.

(References: Arcana Coelestia 5371, Genesis 41; Mark 10)