如何理解这句话（请教各位考南大英语语言学的研友）

如何理解这句话（请教各位考南大英语语言学的研友）
陈新仁教授的《英语语言学实用教程》中P20 推荐材料讲到语言的任意性时有这样一句话有些复杂，请教一下各位这句话的结构以及该如何理解？“On the contrary, it is precisely because linguistic forms do not resemble what they signify that they can be used to encode what is significant by convention in different communities.”