It means that though the Witch knew the Deep Magic, there is a magic deeper still that she did not know. Her knowledge goes back only to the dawn of Time. But if she could have looked a little further back, into the stillness and darkness before Time began, she would have read there a different incantation. She would have known that when a willing victim who had committed no treachery was killed in a traitor's stead, the Table would crack and death itself would work backwards.
C. S. LewisIt is quite useless knocking at the door of heaven for earthly comfort. It's not the sort of comfort they supply there.
C. S. LewisThe difference [God's] timelessness makes is that this now (which slips away from you even as you say the word now) is for Him infinite.
C. S. Lewis