Both of these sonnets deal with the theme of love. In both poems, the speakers are trying to communicate their emotions to their loves. In Shakespeare's sonnet, the speaker is saying that even in the worst of circumstances, thinking of his love makes him feel more stately than a king. In Spenser's sonnet, the speaker writes of his attempts to immortalize his love, a task he will complete by writing enduring poetry of their love.
Shakespeare and Spenser both employ hyperbole in their poetry. In Sonnet 29, the speaker's claim of his love raising him to the feeling of a king is a great exaggeration. Similarly, in Sonnet 75, the speaker's claim to make their love immortal is an exaggeration. Shakespeare also uses simile in his sonnet ("Haply I think on thee, and then my state, I, by chance, think of you and then my melancholy Like to the lark at break of day arising"), whereas Spencer uses personification ("But came the tide, and made my pains his prey"). Both writers use figurative language to create vivid images and emotions.