The 217th mitzvah is that in a case when a yavam1 will not marry his yevamah,2 she performs chalitzah3 on him.
The source of this commandment is G‑d's statement4 (exalted be He), "She shall remove his shoe from his foot."
The details of this mitzvah are found in the tractate devoted to this subject, tractate Yevamos.
You are already familiar with the statement of our Sages,5 "Performing the mitzvah of yibum [i.e., marrying the yevamah] is preferable to performing the mitzvah of chalitzah."6
For this same reason7 they called the tractate "Yevamos,"8 even though it gives equal coverage both to the laws of yibum and those of chalitzah.
