when you eat and are full

"when you have enough food to eat"

your heart will be lifted up

Here "heart" represents the inner person. To become prideful and no longer obey Yahweh is spoken of as if the person's heart is lifted up. Alternate translation: "you will become prideful and no longer obey Yahweh" (See: rc://en/ta/man/translate/figs-metonymy and rc://en/ta/man/translate/figs-metaphor)