The phrase "are one obligation" can be expressed in different ways using synonym replacements. "Are one duty" has a similar meaning, emphasizing a sense of responsibility or moral obligation. "Are one responsibility" carries the same connotation, stressing the necessity of fulfilling a given task or undertaking. Meanwhile, "Are one mandate" places greater focus on a command or directive, indicating that the obligation is not optional, but mandatory. Other synonyms for the phrase include "Are one commitment" and "Are one pledge," both of which emphasize a sense of dedication or promise to fulfill an obligation. Ultimately, the most appropriate synonym will depend on the exact context in which the phrase is being used.