What is the theme of Mary, Lady Chudleigh's poem "To the Ladies"?

It's an interesting poem, I think. And it's theme is set out in its first couplet:

WIFE and servant are the same,
But only differ in the name...

A wife and a servant are the same thing, Chudleigh argues. Why? Because once they've been married, and said "the word obey" (the marriage service calls for women to love, honor and obey), the husband changes. "All that's kind" in him disappears, and

Fierce as an eastern prince he grows,
And all his innate rigour shows :
Then but to look, to laugh, or speak,
Will the nuptial contract break.

"Rigour" is cruelty. And this cruel husband believes that his wife looking, laughing or speaking breaks the marriage contract. How is a wife to behave then?

Like mutes, she signs alone must make,
And never any freedom take :
But still be govern'd by a nod,
And fear her husband as a God...

Finally, Chudleigh's poem addresses itself directly "to the ladies":

Then shun, oh ! shun that wretched state,
And all the fawning flatt'rers hate :
Value yourselves, and men despise :
You must be proud, if you'll be wise.

Women should shun the "wretched state" of marriage, and hate all men who flatter and fawn. Instead, they should value themselves, and be proud, and wise.

The theme of the poem then, is why men are evil - and why women shouldn't marry them. Quite forward-thinking for 1703.