Because it tells the depth of maternal love and the voice of wanderers for thousands of years. Missing relatives is the concentrated intention of officials and students studying abroad. Inch grass heart, wrote his own tie to his mother, Sanchunhui wrote the breadth of maternal love. The contrast method highlights the theme and the antithesis sentence is catchy. Today is of greater significance, which can refer to alma mater, hometown, motherland and so on. So it is widely sung.