what the author wants to say here?:

[princehamlet]

what is the meaning of bold sentences?

O white Bianca, lovely as the moon, The light of thy pure soul and shining wit Shows me my shame, and makes the thing I was
Slink like a shadow from the thing I am.

B I A N C A

Let that which casts the shadow act, my lord, And waste no thought on what its shadow does Or has done. Are youth, and strength, and love Balked by mere shadows, so that they forget Themselves so far they cannot be recalled ?

[Pompey Bum]

Makes the thing I was slink like a shadow from the thing I am = makes my bad former self flee in shame from the good person I have since become.

Let that which casts the shadow act, my lord, And waste no thought on what its shadow does Or has done. Are youth, and strength, and love Balked by mere shadows, so that they forget Themselves so far they cannot be recalled ?

= Then let your true self do (something) and not worry about what your darker self has done (or is doing), because your good side can't be permanently put off by your bad side.