The nature of a thesis statement is that it asserts a specific and unique idea that the writer has regarding the literary (or other) text under discussion. Let's start by clarifying the nature and definition of a thesis.

• (1) A thesis addresses a stated aim and purpose for writing an essay: [purely made-up hypothetical example] I hope to clarify the question of the validity of Spenser's bird metaphors for the purpose of encouraging further research.
• (2) A thesis presents a Big Idea you have been inspired with pertaining to the text as a result of your reading and research: [purely made-up hypothetical example] Spenser's use of bird metaphors contradicts the meaning of the sonnets where used and turns them against themselves creating internal binaries.
• (3) You must prove this Big Idea with textual evidence and sound analysis, using research as an added tool for doing so.
• (4) Your thesis must assert an argument to be proven or ask a question to be explored through analysis and answered. [Argument here means a critical discussion of opposing views.]
• (5) A thesis is by nature contentious, that is, not everyone who reads your thesis (and essay) will be disposed to agree with you because you have seen or thought something as a result of your analysis and research that is not readily obvious to others.

So, in order to get started on your essay, which you are correct in thinking requires the formation of a thesis, you must have a flash of inspiration based on your reading of the Amoretti and form your Big Idea that can be argued and proven and that others may not readily agree with; it may be posed as a question or an assertion. From this, you will be able to clarify your aim and purpose, formulate your structure, accumulate points for your argument and for opposing views, and draft your essay.

Sweet be the bands, the which true love doth tye,
without constraynt or dread of any ill:
the gentle birde feeles no captivity
within her cage, but singes and feeds her fill. (Amoretti, SONNET LXV)