In the Bible (and in life), the idea of withering is usually connected to plants, and plants generally wither if they don't get enough water. Plants represent individual facts and thoughts, and water represents natural truth, or true concepts about life on an external level. To wither, then, generally means that disconnected ideas will not be remembered and will be useless if they are not sustained by deeper concepts that lead to good actions in life.

To wither, as in Psalm 1:3, means to dry up, or to lack good and truth. (Apocalypse Explained 419).

In Psalm 102:4, this signifies that the truths of good seemed to be dying. (Apocalypse Explained 403[6])

'Withering and drying up,' as in Ezekiel 17:10, referring to the east wind, signifies a state when there is no good or truth.

In Matthew 13:6, "wither" signifies the truths of good adulterated and dying. (Apocalypse Explained 401[35]).

Withering, as in Matthew 21:19, signifies the failing of truth and good in the natural. (Apocalypse Explained 403[21]).

(References: Arcana Coelestia 6693 [2], 6726, 8699, 8902 [6]; The Apocalypse Explained 518 [12], 627 [9])

8699. 'You will surely wither away, both you and this people who are with you' means that if it carries on as before the truth which has been implanted is going to perish. This is clear from the meaning of 'withering away' as being consumed little by little, and so perishing. The reason why it is the truth that has been implanted is that 'Moses' is used to mean the truth from God, and 'people' those who receive it. More about all this will be stated in what follows below.