The soverayne beauty which I doo admyre,
witnesse the world how worthy to be prayzed:
the light whereof hath kindled heavenly fyre,
in my fraile spirit by her from basenesse raysed.
That being now with her huge brightnesse dazed,
base thing I can no more endure to view:
but looking still on her I stand amazed,
at wondrous sight of so celestiall hew.
So when my toung would speak her praises dew,
it stopped is with thoughts astonishment:
and when my pen would write her titles true,
it ravisht is with fancies wonderment:
Yet in my hart I then both speake and write
the wonder that my wit cannot endite.
Even though the poet’s eyes, mind, and inner life stand in awe of the physical and spiritual beauty of the woman, he insists that he will write – unlike some such poems that end in a kind of despair. 
 From Flinker’s  The Song of Songs in English Renaissance Literature: Kisses of their Mouths  (2000) p. 71: 
 Spenser’s sonnet concludes, not unlike  Cavalcanti’s , with a treatment of the poet’s view of his own inability to express what he has experienced. … It is significant that Spenser’s version of Cavalcanti’s predicament includes the poet’s ability to capture both speech and writing in his ‘hart’ if not with his pen. That is, Spenser’s poem is part of the initial concern of the  Amoretti  with literature and poetic inspiration. The poem rephrases the despair of Cavalcanti at articulating his wonder with a determination to have ‘hart’ direct ‘wit’ which has been amazed at the lady and her light.
Amoretti: Sonnet 3