a man is ethical only when life, as such, is sacred to him, that of plants and animals as that of his fellow men, and when he devotes himself helpfully to all life that is in need of help.

슈바이처 명언이라고 하는데
도저히 문장 해석을 못하겠어요..ㅠㅠ
특히 that of plants~의that을 어떻게 해석해줘야 할지도 모르겠구요..ㅠㅠㅠ
도와주세요...