Harmony is not invisible in the relevant sense, so it could still be true that invisible things can't be destroyed, since the soul is invisible in that sense, it would follow the soul can't be detroyed.

和声在这个意义上不是无形的，所以无形的东西不能毁灭,仍然可以是正确的，因为灵魂在这个意义上仍是无形的，你可以得出灵魂不能毁灭的结论。

耶鲁公开课 - 死亡课程节选