What does Deuteronomy 11:18 mean?

I will give grass in your fields for your livestock, and you shall eat and be full.

Be careful, lest your heart be deceived, and you turn away, and serve other gods, and worship them;

and Yahweh’s anger be kindled against you, and he shut up the sky, so that there is no rain, and the land doesn’t yield its fruit; and you perish quickly from off the good land which Yahweh gives you.

You shall teach them to your children, talking of them, when you sit in your house, and when you walk by the way, and when you lie down, and when you rise up.

You shall write them on the door posts of your house, and on your gates;

that your days may be multiplied, and the days of your children, in the land which Yahweh swore to your fathers to give them, as the days of the heavens above the earth.