Courtesy is the expression of consideration for others. The military has left little to chance and thus has distinctive and concise expressions of military courtesy. To give merely a perfunctory or grudging display, or worse yet a slovenly display, even if the motions are technically correct, is in fact discourteous.
One must remember that the courtesy which marks military ceremonies has a profound meaning. A salute to the flag is not an upper body exercise or just another annoying rule to follow, it is a declaration of loyalty to these United States and to the principles of liberty and justice on which the Nation was founded.
When a military person presents arms at retreat or salutes a senior, it is a recognition of the organized authority of the Nation, as represented by the military services which are charged with its protection.
Since antiquity, men of arms have rendered some form of salute as an exchange of greeting. Although the origins of saluting have been lost, since as early as the Age of Chivalry, it was in common practice. During that period, the knights were mounted and wore steel armor and mail which completely covered their body.
When two friendly knights met, it was the custom for each to raise his visor and expose his face to the other. This was always done with the right hand. It was a significant gesture as it exposed the features and also removed the right hand- the sword hand- from the vicinity of the weapon.
Later, during the Middle Ages, men of means often wore heavy capes under which swords were carried. Upon meeting a friend, the cloak was thrown back by raising the right hand, thus disclosing that the right hand was not on the sword hilt.
These gestures came to be recognized as proper greeting among soldiers, and were continued even as swords and mail became a thing of the past. The military salute is today, as it has been for ages, a unique exchange of greeting between military men and women.