All things that pass
Are woman's looking-glass;
They show her how her bloom must fade,
And she herself be laid
With withered roses in the shade;
With withered roses and the fallen peach,
Unlovely, out of reach
Of summer joy that was.
All things that pass
Are woman's tiring-glass;
The faded lavender is sweet,
Sweet the dead violet
Culled and laid by and cared for yet;
The dried-up violets and dried lavender
Note that lavender symbolises maturity, grace and elegance. So this line is saying that, even if faded, the lavender has positive attributes. 
 The repetition of ‘sweet’ at the end of one clause and the beginning of the next is a device known as  anadiplosis . The effect is to build drama. 

Passing And Glassing