This has nothing to do with the First Amendment – the Free Exercise Clause concerns solely the relationship between government and those governed, not between or among private persons and private entities; in this case between a private employer and employee.
This case concerns the provision of the CRA prohibiting employers from discriminating against employees because of their religion – such as employers refusing to hire Jewish employees or firing an employee because he’s a Muslim.
But the courts have recognized a limit to the extent an employee must accommodate an employee’s religious beliefs, such as placing an undue burden on the ability of a business to function, and appropriately so.
Unfortunately this conservative Court, obsessed with subjecting private employers to the tyranny of religious dogma, will likely rule in favor of Goff, hidden behind the façade of ‘religious liberty.’
The United State Postal Service is owned by the United States Government and is not a "private employer" by any stretch of the imagination.