Sefer HaChinuch (#430, toward the end) says: “Anyone who is careful in Birchas HaMazon [the blessing after the meal] will have his sustenance come to him with honor his entire life.”
If most of us were honest with ourselves, we’d admit that we are probably not as careful as we should be in bentching. We are even likely skipping words. We fool ourselves into thinking we know it by heart. Do you want sustenance with honor your entire life? Start saying Birchas HaMazon slowly and carefully from a siddur or a bentcher.
Excerpt from “Perspectives of the Maggid .”