关于英语分词做后置定语和be to do 结构的疑问

1.conveyed的用法是正确的,英语中有三类词是非谓语动词：不定式,动名词和过去分词,动名词表主动,而过去分词表被动,在the symbolic meanings subtly conveyed中,主语与动词是被动的关系,那么为什么用非谓语动词呢,很简单,除了复合句和几个谓语同时并列的情况,一个句子只能有一个谓语动词,后面的 should be taken 就是这句话的谓语,而subtly conveyed 只是作定语修饰前面的主语,同时这句话我们可以把它改成一个定语从句：the symbolic meanings which are subtly conveyed should be taken more seriously.这样应该好理解了吧?
2.be to do是不定式作表语,不定式作表语表示具体动作或将来动作,如：
My work is to clean the room every day.
His dream is to be a doctor.