Where the NRSV has "be their shepherd" in this verse, the Geneva Bible and the King James Version translate this as "feed them." The actual Hebrew uses "shepherd" as a verb, so either is acceptable. But in this case, the more modern translation helps bring home the rôle God plays in our lives. A shepherd doesn't just feed, but also guides and protects.
Good Shepherd of the sheep, by whom the lost are sought and guided into the fold; feed us and we shall be satisfied, heal us and we shall be whole, and lead us that we may be with you, with the Father, and the Holy Spirit. Amen.
—A New Zealand Prayer Book