Part of the procedure for the release of the widowed wife (without children) from her status of connection to her brother-in-law involves the removal of his shoe and then spitting before the brother-in-law in front of the Bais Din. The commentators provide many reasons for these actions:
Chinuch
The widow was prepared to wed her brother-in-law and serve him as her husband in order to attempt to continue her deceased’s husband name. The brother-in-law does not wish to marry her. Therefore, she first performs a marriage-service to the brother-in-law of removal of his shoe to show the Bais Din that she is willing to marry him. Then she performs a disgusting act of spitting in front of him to show that her possible connection to the brother-in-law is completely severed.
Pane’ach Raza
At first the widow bows down to her brother-in-law requesting that he marry her, and she would serve him even to the level of removal of his shoes. And after he refuses to marry her, she spits in front of him to express that he should be considered as disgusting as spit.
Mincha Belulah
The brother-in-law’s refusal to marry the widow prevents the building of the house of his brother. Thus, the widow takes off his shoe expressing that she was willing to serve him like a maid servant. However, as a result of the refusal to marry her, she spits in front of him to show that she is not concerned about herself, rather about her dead husband, and his brother should now be treated as if he was dead.
R’ Bachaye (1)
As long as the brother-in-law wishes to marry the widow, it is as if the brother is still alive (due to possible future offspring). When the brother-in-law refuses, then it is as if the brother is finally dead and his brother refused to mourn him. Therefore, the widow removes the shoe to express that the brother-in-law should be in mourning (and not acting like he has forgotten and buried his brother). The spitting in front of the brother-in-law is to publicly shame him for his refusal.
R’ Bachaye (2)
The brother-in-law that refuses is like a brazen person since he doesn’t wish to help the soul of his brother. Removal of his shoe expresses his disdain for his brother that he has been removed from his “brotherhood.” He has removed (חלץ) himself and closed (נעל) the door on the soul of his deceased brother. And the shoe is removed from his foot to indicate that he is the cause of the movement (רגל) of his brother’s soul from his family. And she spits to allude to his lack of commitment to use his fluids to help his brother.
Baha”g
The brother-in-law who refuses to perform his mitzvah is as if he is rebelling against the concept of Mitzvos from Sinai. He is to be treated as someone who is in cherem, removed from society and not allowed to wear shoes.
Malbim
The main concept that differentiates between humans and animals is freedom of choice. Humans choose to wear shoes (made from animal skin) that show that humans select where they go. The Torah commands this mitzvah of Yibum which is counter to normal thought, and the brother-in-law refuses to use his free choice and follows his natural tendencies. Thus, he is no longer different than the animals (who follow their nature) and does not need to wear shoes.
Tzror HaMor
The deceased’s soul remains connected to the widow and is not able to be released from this world unless she has a child from the brother-in-law, or the procedure of Chalitzah removes him from this world. The removal of the shoe from the brother-in-law releases the spirit from the wanderings in this world; and the spit from the widow releases the final connection of the soul to her, enabling the soul’s release and departure to other places.
