This teaches us an important lesson in human nature and the service of the divine.
We aren't G-d. We don't have the vision necessary to perceive the wholeness or lack thereof by purely spiritual standards. We, therefore, must rely on the vision that Hashem created us with.
The kohain who has lived his life with a limp due to a leg injury that has healed wrong may very well be a pure and perfect servant of the creator; but he may not be MY appointed messenger. In my eyes ( limited as they are ) he is imperfect – I must heed my eyes and disqualify him. For choosing him despite his imperfection would be belittling the divine service in its entirety.
And us ? When we do a mitzvah – do we neglect a cosmetic detail with the understanding that "רחמנא ליבא בעי" ("The Merciful One desires [service from] the heart") ? Yes, our service should be more than skin deep and meaning is more important that looks – but - we shouldn't allow ourselves to compromise on the beauty of a mitzvah either – it may very well bring our service down a notch.Hatzlacha !!