It is difficult to tell what or who should provide for retired workers in the future.

provide 是动词，意思是"提供、供给"，指给予所需的东西或服务。 for 在这里是介词，表示"为...（某人或某事）"，引出受益的对象。 provide for 是一个固定短语，意思是"为...提供生活所需"或"供养"，特别指为某人提供经济支持或生活保障。