This sonnet is part of the Astrophel and Stella sequence of sonnets by Sir Philip Sidney, which chart the struggle of the speaker to embrace his emotions for his lover. This sonnet focuses on the way in which, in addition to the pain of having to cope with his feelings of love for the object of his affections, the speaker must also "contend" with the idea that "Desire / Doth plunge my well-formed soul even into the mire / Of sinful thoughts." Given the way that the speaker is currently struggling so much with his passions and love, he finds this thought very annoying, as is shown by the conclusion of this poem:
If that be sin which doth the manners frame,
Well stayed with truth in word and faith of deed,
Ready of wit and fearing nought but shame;
If that be sin which in fixt hearts doth breed
A loathing of all loose unchastity,
Then love is sin, and let me sinful be!
The poem thus concerns the beauty of loving and how good and pure such love is. Any attempt to persuade somebody that love is actually sinful and something to be wary and suspicious of is therefore automatically debunked. Love does not necessarily lead to "loose unchastity," and if it does, then the experience of love is so wonderful that the speaker will glady brand himself with the title of a "sinner."