The word "sheep" is a metaphor for the followers of Jesus. The metaphor of Jesus as the "shepherd" is also implied. AT: "Just as sheep obey the voice of their true shepherd, my followers heed my voice" (See: [[rc://en/ta/man/translate/figs-metaphor]])
Here the word "hand" is a metonym that represents the protective care of Jesus. AT: "no one will steal them away from me" or "they will remain secure forever in my care" (See: [[rc://en/ta/man/translate/figs-metonymy]])