Read this excerpt from frederick douglass’s speech “the hypocrisy of american slavery.”

fellow citizens, pardon me, and allow me to ask, why am i called upon to speak here today? what have i or those i represent to do with your national independence? are the great principles of political freedom and of natural justice, embodied in that declaration of independence, extended to us? and am i, therefore, called upon to bring our humble offering to the national altar, and to confess the benefits, and express devout gratitude for the blessings resulting from your independence to us?

would to god, both for your sakes and ours, that an affirmative answer could be truthfully returned to these questions. then would my task be light, and my burden easy and delightful. for who is there so cold that a nation's sympathy could not warm him? who so obdurate and dead to the claims of gratitude, that would not acknowledge such priceless benefits? who so stolid and selfish that would not give his voice to swell the hallelujahs of a nation's jubilee, when the chains of servitude had been torn from his limbs?

what effect is achieved by using a series of questions in this speech?