Though the approach of the women in these poems is decidedly different in how each welcomes (or not) the amorous advances of a [would be] lover, the theme revolves around the "Carpe Diem" (Seize the Day) line of thought, to embrace the moment.
In Andrew Marvell's "To His Coy Mistress," the speaker encourages the object of his affections to give in to his wooing, for he speaks of how quickly time flies:
But at my back I always hear
Time's winged chariot hurrying near;
And yonder all before us lie
Deserts of vast eternity.
For the speaker, the idea is not just that they only have a limited time together perhaps for that moment or that day, but that eternity is not far behind. He further presses his suit by explaining that they will not always be as they are, but will lose the blush of youth, and what a shame for her to go to her death, wasting her virginity and taking it to her tomb.
Thy beauty shall no more be found,
Nor, in thy marble vault, shall sound
My echoing song; then worms shall try
That long preserv'd virginity,
And your quaint honour turn to dust,
And into ashes all my lust.
The message found in Aphra Behn's poem, "The Willing Mistress," speaks to two lovers who are both eager to act upon their passion. They are aware of the beauties of nature around them, perhaps lending itself to the sense that their physical love is natural, and therefore at home amid the "Winds that gently rise..." and the sun shining on them through the branches.
The speaker says that for each touch her lover offers, she returns the same to him ("A many Kisses he did give / And I return'd the same,") but she is only reticent to speak specifically of what they do rather than to do it, as was Marvell's "coy Mistress." The speaker's willingness to continue is also described in:
His Charming Eyes no Aid requir'd
To tell their softning Tale;
On her that was already fir'd,
'Twas Easy to prevaile.
Whereas the speaker in the first poem expresses the desire to consummate their love while they still may, the speaker in the second poem embraces the situation without hesitation.
The theme I hear in both is to live in the moment, to seize the moment and live life to the fullest; the speaker in the first poem speaks to fulfilling this desire, and the speaker in the second poem does fulfill the desire.