For those who have not read the book, some context for the quote below. Running away from some school bullies, Jill and Eustace find themselves in Aslan's country, high, high above and far, far away from Narnia. The pair are dramatically separated, with Eustace ending up in Narnia. Aslan sends Jill on a quest to find Eustace and inform him of a quest both of them must undertake.
Before sending Jill to Narnia, Aslan shares with Jill "four signs" that will guide her and Eustace on their quest. Jill must remember these signs if they are to be successful. Much will go wrong should Jill forget. So Aslan drills Jill, asking her to repeat the signs over and over, until she's got them firmly memorized. Having accomplished this, before sending Jill down into Narnia from the heights of his country, Aslan gives Jill this final encouragement and warning:
“But, first, remember, remember, remember the signs. Say them to yourself when you wake in the morning and when you lie down at night, and when you wake in the middle of the night. And whatever strange things may happen to you, let nothing turn your mind from following the signs. And secondly, I give you a warning. Here on the mountain I have spoken to you clearly: I will not often do so down in Narnia. Here on the mountain, the air is clear and your mind is clear; as you drop down into Narnia, the air will thicken. Take great care that it does not confuse your mind. And the signs which you have learned here will not look at all as you expect them to look, when you meet them there. That is why it is so important to know them by heart and pay no attention to appearances. Remember the signs and believe the signs. Nothing else matters.”
Hear, O Israel: The Lord our God, the Lord is one. Love the Lord your God with all your heart and with all your soul and with all your strength. These commandments that I give you today are to be on your hearts. Impress them on your children. Talk about them when you sit at home and when you walk along the road, when you lie down and when you get up. Tie them as symbols on your hands and bind them on your foreheads. Write them on the doorframes of your houses and on your gates.
When the Lord your God brings you into the land he swore to your fathers, to Abraham, Isaac and Jacob, to give you—a land with large, flourishing cities you did not build, houses filled with all kinds of good things you did not provide, wells you did not dig, and vineyards and olive groves you did not plant—then when you eat and are satisfied, be careful that you do not forget the Lord, who brought you out of Egypt, out of the land of slavery.