In Hamlet, what is the main message conveyed by Shakespeare in the "Look here upon this picture" speech?

Let us remember that
this speech is the first time thatis able to confront his mother openly afterhas just discovered
that instead of killing , as he had hoped, he has actually killed the eavesdropping . It is now
that Hamlet is able to release all his long-repressed anger and frustration at his mother. This
speech, therefore, informsof the true nature of her new husband whilst remembering the virtues
of the first, before moving on to lambast her for her decision to marry Claudius.

The old Hamlet is described as having "the front of Jove himself," whereas in
the picture that Hamlet is painting for his mother, and they have just seen enacted by ,
Claudius, her new husband, is "like a mildew'd ear / Blasting his wholesome brother."
The speech turns into a bitter attack on Gertrude for her impropriety of marrying such a man
after her first husband, and ends with a denunciation of her act:

O shame! where is thy blush? Rebellious hell,

If thou canst mutine
in a matron's bones,

To flaming youth let virtue be as wax,

And melt in her own fire: proclaim no shame

When the compulsive
ardor gives the charge,

Since frost itself as actively doth burn

And reason panders will.

Hamlet questions what
led her to marry again, and laments the shame that caused her to act so terribly and then
finally asks evil to melt his own bones because of the heinous nature of her
act.