«As an unperfect actor on the stage
Who with his fear is put besides his part».
Most of Sonnet 23 compares the poet’s role as a lover to an actor’s timidity onstage. The image of the poor theatrical player nervously missing his lines is the first indication that the poet doubts whether his love for the young man is requited.
As an unperfect actor on the stage
The first two lines of the sonnet, “As an unperfect actor on the stage,/ Who with his fear is put besides his part,” are linked with the first two lines of the second quatrain, “So I, for fear of trust, forget to say/ The perfect ceremony of love’s rite.” The line “More than that tongue that more hath more expressed” hints at thedebased language of a rival poet — like the rival in Sonnet 21. The parallel to this rival poet’s abundant language is the poet’s excessive love, a passion that, without a doubt, ties his tongue, destroys his confidence, and humbles him.
English audio from YouTube Channel Socratica
Summary from Cliffsnotes.com