order of witch they speak- first represnet past, ehere macbeth is already this, second is present, macbeth has been made this(doesnt know it yet- dramatic irony) third represent future where he will be king- mythalogical allusion to the tree fates of greek mythology- similialy controlled mortals past present and future
shaspears is suggesting that macbeths path may have already been mapped out or fated
provide no insight on how he will achieve this- it is macbeth that quickly condiders muder as the only way he could possibky become king