不可以省略.
that are的前面是motives,也就是说,“that are of varying importance to different people”是形容motives的.
用一个简单的例子来解释：It is with her help that I manage to score A1.这句话里的“that I manage to score A1”是形容有了她的帮忙之后的结果.
亲之所以觉得应该去掉,是否是因为觉得of motives that are of varing importance念起来很奇怪?
of varying importance是个词组,它同等与very important.
importance是noun.所以加了of在前,而important是个adj.可以直接用在is,are,be的后面.
举个例子：
Having a paper qualification are important to people living in that country.
同样,你可以说：Having a paper qualification are of varying importance to people living in that country.
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P.S：【这一段可不看,只是额外的小知识】
除了of varying importance,你可以用of paramount importance.【个人觉得后者会更显品质?.】用刚刚的例子：Having a paper qualification are of paramount importance to people living in that country.
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看的会不会太乱?.
希望以上答案能够帮到您.