Of Shakespeare's 154 known sonnets, the first 126 are addressed to a young man. Sonnet 20 is complex in that it is very clearly a love poem, yet there is an acceptance that it is a love that will not ever be fully realized.
A woman's face with Nature's own hand painted
Hast thou, the master-mistress of my passion;
The opening lines let us know who the poet is addressing. By saying "master-mistress," we know that the subject of the sonnet is a man, and based on the description, we can infer that the man is beautiful and likely feminine in his features. However, the poet goes on to describe the ways in which this young man is better than any woman. His heart is gentle like a woman's heart, but it is not false or changeable like women's hearts. His eyes are brighter than a woman's eyes and they have a constancy that women's eyes lack. The man's eyes are so bright that they "gild" those that he looks upon (gild literally meaning to coat in gold or some precious metal - so, his eyes bring light and value to those in his view).
The line "A man in hue, all hues in his controlling" is interesting in its rhetorical construction. Shakespeare is saying that the man is a true man in his physical form and all other men are under his control. He uses the word hue the second time in place of the word men. A hue is a tint or a shade of color - by using the word hue in place of men, it indicates that all other men are but tints or shades of this one. The object of the poet's affection captivates both male and female attention.
Here, the sonnet takes an interesting turn. The poet argues that the young man was intended to be a woman, but he was so beautiful that personified Nature herself fell in love with him and added one thing (male genitalia) and made him a man, "thus defeating" the poet. He cannot ever fully have the man due to the fact that they are both men. The poet sees it as a selfishness on the part of Nature.
There is an acceptance in the final rhyming couplet.
But since she prick'd thee out for woman's pleasure
Mine be thy love and thy love's use their treasure.
There is nothing the poet can do to change the gender of his love, yet he contents himself with a spiritual or emotional relationship - the truest, purest love - with the young man and accepts that only women will enjoy the physical pleasures to be had in the relationship. The word "pricked" is at once a play on the word "picked" and a crude reference to the male anatomy. The treasure that he is referring to is the man's body. There is a conflict in the poet. He wants to enjoy fullness in love with the object of his affections, yet the poet has feelings of acceptance on the supposed "laws of nature" that will prevent a full relationship. He is happy enough that he can enjoy an emotional relationship with the man, even if he can never enjoy his body.