"theirs not to reason why, theirs but to do or die." why did the use these words? based on tennyson's choice of words, what was he saying about the soldiers' commitment to battle?

Asap plz which sentence from this excerpt of jefferson davis’s inaugural address indicates that secession was the confederacy’s way of reclaiming its legal powers? an agricultural people, whose chief interest is the export of a commodity required in every manufacturing country, our true policy is peace, and the freest trade which our necessities will permit . . there can be but little rivalry between ours and any manufacturing or navigating community, such as the northeastern states of the american union. it must follow, therefore, that a mutual interest would invite good will and kind offices. if, however, passion or the lust of dominion should cloud the judgment or inflame the ambition of those states, we must prepare to meet the emergency and to maintain, by the final arbitrament of the sword, the position which we have assumed among the nations of the earth. we have entered upon the career of independence, and it must be inflexibly pursued. through many years of controversy with our late associates, the northern states, we have vainly endeavored to secure tranquillity, and to obtain respect for the rights to which we were entitled. as a necessity, not a choice, we have resorted to the remedy of separation; and henceforth our energies must be directed to the conduct of our own affairs, and the perpetuity of the confederacy which we have formed. if a just perception of mutual interest shall permit us peaceably to pursue our separate political career, my most earnest desire will have been fulfilled. but, if this be denied to us, and the integrity of our territory and jurisdiction be assailed, it will but remain for us, with firm resolve, to appeal to arms and invoke the blessings of providence on a just cause . .