the realization that assignments are a metalevel change from functions, and therefore should not be dealt with at the same level I have no idea what Kay himsel

the realization that assignments are a metalevel change from functions, and therefore should not be dealt with at the same level I have no idea what Kay himself meant by this, but I personally appreciate that they are very different (and maybe my perspective aligns with his). A function prescribes how to transform input data and produce output data. An assignment manipulates the environment of the scope itself - you are updating some state somewhere in the runtime, the interpreter or main memory.