«Sin of self-love possesseth all mine eye
And all my soul and all my every part».
The poet thinks of himself as a young man and condemns his own narcissistic vanity. Unfortunately, although he can intellectualize narcissism as an unworthy attribute, nonetheless “It is so grounded inward in my heart.”
Sin of self-love possesseth all mine eye
This youthful image of himself is abruptly shattered in lines 9 through 12, beginning with the typical “But,” when the poet looks at himself in a mirror and sees his true self, “Beated and chopped with tanned antiquity.” Swinging between this antithesis of youth and old age, the poet’s narcissistic self-love makes him guilty of his young friend’s vice: “Tis thee, myself, that for myself I praise, / Painting my age with beauty of thy days.” While he condemns vanity in the youth, he admires it in himself. The phrase “for myself” means that he has assumed the youth’s identity, and the problem of the youth’s identity remains one of vanity. As is evident in later sonnets, the poet is preoccupied with the idea of personal identity.
English audio from YouTube Channel Socratica
Summary from Cliffsnotes.com