The theme of "Blame Not My Lute" is in keeping with the courtly love poetry that he learned while on a diplomatic trip to Italy and tells of love within the "love is like war" Petrarchian love conceit. The lute player, and speaker of the poem, has changed his tune to match the lady's changed behavior; the music sounds not so sweet to her as formerly, but this is because her behavior seems not so sweet to him as formerly.
The Lady's response is to break the strings of his lute. The speaker advises her to cease doing that, informing her that when she changes back to her former ways, the music from the lute will undergo a corresponding change and be sweet to her once again. Wyatt is expressing the theme that blame can't be attributed to someone--or something else--when a person is faced with the results of a change in them that leads to dishonorable and unloving behavior: blame not my lute, blame yourself.
Wyatt uses personification for the lute and strings, giving human attributes of action and volition: "he must agree," "they must obey," "My lute and strings may not deny." Wyatt isn't known for metaphor and simile or sensory related imagery (what things taste, feel, smell like), but here, he does refer to what the flute sounds like "be somewhat strange," "be somewhat plain." He also uses figure of speech scheme techniques such as epanalepsis in "spite asketh spite" and repetition in repeating the ending line "Blame not my lute!" in each stanza as well at the start of the first stanza. There are six stanzas of a sextain and repeating ending line. The rhyme scheme is ababcc d.