We must believe that we have the ability to change our ways. The Gemara (152.) states, איניש בר בריגלוהי ודמנעלי, when a person wears shoes, he is a human being. Without shoes, he isn't a human.
The Malbim explains. What is the difference between people and animals? If you say it is the power of speech, animals also have some form of speech. If you say that it is intelligence, animals also have intelligence (see Iyov 35:11). So, in what way is a person better than an animal? It is because a person can go against his nature, and an animal can't.
The Malbim further clarifies that shoes separate us from the earth. Shoes demonstrate that we are not bound to act according to the rules of nature. We can elevate ourselves above the earth, above the pull of nature and the yetzer hara. Therefore, someone who doesn’t wear shoes isn’t considered human. He lacks the defining quality that humans have over animals.
When chalitzah is performed, the widow removes the yavam's shoe, as stated in this week's parashah (25:9) רגלו מעל נעלו וחלצה. This is done when a yavam refuses to do the mitzvah of yibum (the preferred mitzvah). He isn't able to go against his nature, so he is similar to an animal. He couldn't elevate himself above the earth, so he should go without shoes.
