Here "good shepherd" is a metaphor that represents Jesus. Alternate translation: "I am like a good shepherd" (See: [[rc://en/ta/man/translate/figs-metaphor]])
To lay down something means to give up control of it. To lay down one's life is a mild way to refer to dying. Alternate translation: "dies" (See: [[rc://en/ta/man/translate/figs-euphemism]])