In this passage, former President Kennedy's purpose is to argue that the excessive expenditure of billions of dollars every year on weapons, which are acquired for the purpose of making sure they never need to be used, is not the most efficient means of achieving and maintaining peace. He suggests that there are alternative ways to attain peace and that peace is a rational objective which all rational men should strive for.
Kennedy's purpose is evident in his statement "But surely the acquisition of such idle stockpiles-which can only destroy and never create-is not the only, much less the most efficient, means of assuring peace" (7) which is emphasizing that the acquisition of weapons is not the only, nor the most efficient, means of achieving peace.
He also states that "I speak of peace, therefore, as the necessary rational end of rational men" (7) which denotes that peace is a necessary and rational objective that all rational individuals should strive to achieve.
Finally, He also puts a sense of urgency to the task of achieving peace in his statement "But we have no more urgent task." (7) which clearly states his desire to convey the importance of peace and encourage the audience to take action towards achieving it.
Overall, President Kennedy's purpose in this passage is to advocate for a re-evaluation of priorities in regards to military spending and to call for the pursuit of peace as a necessary and rational objective. He urges his audience to prioritize peace and consider alternative methods of achieving it over excessive military spending.
Also, havnt you already asked this question?