What's he saying?
"Whoever hath her wish, thou hast thy Will, / And Will to boot, and Will in over-plus;"
No matter what other women have to satisfy their sexual desires, you have more satisfaction that you even need;
"More than enough am I that vexed thee still, / To thy sweet will making addition thus."
Surely I, who have pleaded with you so insistently, am enough to satisfy you sexually.
"Wilt thou, whose will is large and spacious, / Not once vouchsafe to hide my will in thine?"
Won't you, with your huge sexual appetite, let me have sex with you just once?
"Shall will in others seem right gracious, / And in my will no fair acceptance shine?"
Would you have sex with others, but not with me?
"The sea, all water, yet receives rain still, / And in abundance addeth to his store;"
Even though the sea is totally composed of water, it still lets the rain add more water to it;
"So thou, being rich in Will, add to thy Will / One will of mine, to make thy large will more."
In the same way, although you already are quite sexually satisfied by others, let me also have sex with you.
"Let no unkind, no fair beseechers kill; / Think all but one, and me in that one Will."
Don't hurt anyone who wants to have sex with you by denying them; realize that all penises are the same, and mine should be inside you.
Why is he saying it?
Sonnet 135 and the sonnets that follow play with the different meanings of the word "will;" its surface meaning of volition, or intent, is entirely obfuscated. In fact, if one tries to read it with that meaning, the poem makes little sense. In addition to that surface meaning, the word is used here to mean six other things: lust; the auxiliary verb denoting future tense; determination or willfulness; penis; vagina; the man's name "William." Since "will" can be read as a nickname for "William," the question arises of whom the name refers to. There is general acceptance among scholars that it is the poet himself, but it could also be the woman's husband. It is possible that it could refer to the fair lord, the poet's friend with whom the mistress has also had an affair.
The assumption of this sonnet, that the woman addressed has an insatiable sexual appetite and no discretion when it comes to whom she will have sex with, is unflattering to her. But it is based on the myth that female sexuality poses a threat to societal order. In the Homeric myth, Circe seeks to hold Odysseus in bondage forever as her sexual slave, though it is not explicitly stated. The woman addressed here has "Will to boot, and Will in over-plus," or more sexual partners than she can even handle. The assertion that her "will is large and spacious" implies not just that she has lust enough to go around, but that physically, her vagina has been stretched by so much lovemaking.
Though this sonnet implies that the poet himself is left out of the woman's circle of lovers, lines 3-4 suggest otherwise. They are out of place, since the tone of the sonnet is one of pleading to be allowed to have sex with the mistress, but these lines suggest that he has already been admitted to do so. The term "making addition" means adding his own penis to the line of men who have had access "to thy sweet will." But if his goal has already been achieved, the following lines, which ask, ""Wilt thou, whose will is large and spacious, / Not once vouchsafe to hide my will in thine?" do not make sense. Therefore lines 3-4 can be interpreted as being in question or conditional form, as if he poet is asserting that he would be "more than enough" for her.
Although the theme of this sonnet is clearly sexual, allusions to the Bible are embedded within it. The word "will," around which the sonnet revolves, especially in line 6, "...to hide my will in thine," hints at the phrase, "Not my will but thine be done," from Christ's agony in the Garden of Gethsemane. This comparison aligns the poet with Christ and the mistress with God, suggesting a connection between the mysteries of love and those of religion. Likewise, the word "vouchsafe" used in line 6 is common in the Bible and in prayers, and the word "gracious" is also reminiscent of God's grace.
The meaning of line 13 is somewhat unclear; the second instance of "no" could be meant as a word spoken by the woman in denial of the poet. Or the word "unkind" could be read as a noun, meaning something cruel, or in this case, a refusal of sex. In both these cases, the "fair beseechers" are men such as the poet, "killed" by a refusal. The denial of a lover causing his death is a hyperbole, but there is a double meaning: an orgasm was thought of as a little death. If "kill" is read as meaning "let have an orgasm inside you," then line 13 is an appeal that the woman not have sex with any more "fair beseechers" other than the poet.