This verse illustrates the disadvantage of Arjuna acting contrary to his duty as a ksatriya.

If through injudicious sentiment or bewildered ignorance Arjuna should fail to perform his prescribed duty as a ksatriya by fighting for the sake of righteousness; he would lose a most excellent opportunity of attaining the heavenly spheres, he would lose his reputation as a hero and he would have to accept great sinful reaction.

Now Lord Krishna responds to Arjunas previous distress of not wanting to slay his enemies such as Bhishma and Drona but instead to allow his enemies to slay him. The use of the word atha is to emphasise another point of view that if Arjuna declines to fight this righteous war and chooses to disregard the acquisition of happiness in either this world or the heavenly worlds as enjoined in the Vedic scriptures which state that the royal orders should conquer over his enemies and rule over the earth. Then by refusing to accept his responsibility and avoiding the battle Arjuna would be abandoning his duty which brings rewards and boundless glory and thus losing his reputation both worldly and divine which results from the victory of a great warrior Arjuna would in fact incur great sin.