This verse reveals the intentions of Esau against his brother, Jacob. Because of Jacob's conniving and deceit, Esau has lost both his birthright and his blessing. Esau planned retaliation and revenge against his brother because of the wrongs done to him.
While we can understand his attitude as justifiable, we cannot condone his intentions. Notice the careful planning involved in Esau's scheme. First, he will wait for an appropriate time, when the time of mourning the death of Isaac has passed. Then, he will enact his premeditated plan to slay his brother, Jacob.
The word slay means "to smite with deadly intent". It is the same word used in Genesis 4:8 to describe Cain's murder of Abel.
We note the Source of Esau's determination - "Esau said in his heart..." the seat of desire and inclination. With hatred in his heart, his evil plan is set in motion. Jesus said that it is "out of the abundance of the heart the mouth speaketh." Matt. 12:34. In Matt. 15:19, we read "For out of the heart proceedeth evil thoughts, murders, adulteries, fornications, thefts, false witnesses, blasphemies."
Thankfully, Esau's plan was thwarted and not carried out, due to their mother's intervention, but the intention was there.
Once again, we see that the heart of the matter is a matter of the heart. Perhaps, if we would seek diligently to touch the hearts of our youth with the love of God and implant God's Word in their hearts we would see a change in attitude and actions. All behavior begins in the heart. Proverbs 23:7
J. Edwin Orr based the song "Cleanse Me" on Psalm 139:23, and it carries the thought of today's devotional in the first verse. Take a moment, find a hymnal and give it a singin'.