Through all the thankless years, Cold-edged with dear-bought wisdom, The judgment of your peers!
This particular section is striking to me because it is an acknowledgement by Kipling that what he describes as the "white man's burden", to "civilize" non white societies through cultural, political and economic imperialism, is not considered valid by all white people. Yet, he uses this very fact to further bolster his own narrative, portraying imperialism as a moral necessity precisely due to it's "thankless" nature.