In "To Celia," the lover states in lines 9-12,
I sent thee late a rosy wreath,/Not so much honoring thee/As giving it a hope that there/It could not withered be
Thus, by his own admission, he has sent the lover a wreath of roses, not "to honor" her, but for her to breathe the sweet breath of a lover upon and give it life. When he says that the wreath cannot wither in her presence, the poet conveys the power of the lady. Then, the last four lines of Johnson's poem focus on this power and the lady's interrelationship with nature. For, she gives the wreath immortality as she preserves it with her breath.
Along with immortality of love, the poet clearly suggests the fertility of the one he loves. Her charms become a part of what is around her:
Since when it grows, and smells, I swear,/Not of itself but thee!
The universal purpose and conventional reason why a man gives his lover a rose or a bunch of roses is to convey to her that he is in love with her and desires her to reciprocate his love. Similarly the poet narrator Ben Jonson had been smitten by the beautiful and expressive eyes of Celia so much so that he hyperbolically asserts that he would prefer the left over wine that she has sipped to that of the heavenly nectar of Jupiter itself. So, as a token of his love and in the hope that she would accept his love for her and reciprocate, he sends her not one rose but a garland of roses. Unfortunately for him Celia rejects his offer of love by returning the garland of roses.
Ben Jonson to cover up his embarrassment at her rejection cleverly remarks that although she has rejected his offer of love by returning the wreath of roses he considers himself only too happy and fortunate, because these roses smell more fragrant now and will never fade because they have been revived now by her sweet breath. Although he has not been successful in wooing and winning her he can always console himself with the roses she has sent back to him, because these roses will never fade and wither but on the contrary will continue to grow and smell sweeter than ever before because now they will smell not like ordinary roses but like her sweet breath:
"Since when it grows, and smells, I swear,
Not of itself but of thee."
He says that he sent her the roses knowing that they will never wither away in her presence, but now that her breath has touched them and she has returned them they not only wither away but actually continue to grow. He hyperbolically implies that one breath of hers is enough to make the roses grow forever! !