The birthright belonged naturally to the eldest son of a family. In the case of Isaac, the father of Jacob and Esau, it included not only personal possessions, but also the covenant blessing that God promised to Abraham (Genesis 12:3) and passed on to Isaac. The Abrahamic Covenant was to be transmitted to Isaac’s son. This promise was shared with Rebekah, Isaac's wife, but God additionally told her that “the elder (of the twins, Esau) should serve the younger (of the twins, Jacob).” (Genesis 25:14)
Now recall (1) that the firstborn, Esau, showed very little appreciation for his birthright. He was willing to sell it to Jacob for a bowl of lentil stew. (See Genesis 25:33, 34.) (2) Esau only valued his present life. He showed no faith nor appreciation of the chief feature of the birthright, which was the Abrahamic covenant. (Genesis 25:32.) (3) The line of descent of the covenant (the elder to serve the younger) was treasured by Rebekah, and doubtless communicated to Jacob. Thus Jacob was inspired to find some honorable way to acquire it from Esau. Jacob had faith in the promise of God, in its future fulfillment, and also in God’s message to Rebekah. He saw Esau’s lack of faith and used the opportunity of Esau’s hunger to lawfully purchase the birthright from Esau. Thus Jacob, honestly, came into the inheritance to which God had called him.
(4) Some years afterward (25:27,31; 26:34,35; 27:1-10), Isaac felt he was nearing the end of his life, and he wanted to give the birthright-blessing to Esau. Essentially, Isaac wanted to declare his last will and testament. (27:1-4.) Here Esau should have reminded his father that he had sold his prospective birthright to Jacob, but this he evidently failed to do. Providentially, Rebekah overheard Isaac’s expressed intention, and feared that Isaac would disregard the contract of the birthright sale – if he even knew about it. So she planned the deception. Isaac was misled and bestowed the blessing upon Jacob.
Jacob should not have lied to Isaac by claiming to be Esau. Jacob had lawfully purchased and possessed the birthright. Jacob had a perfect right to receive the blessing. Rebekah, who also aided in the deception, was probably actuated by faith in the promise of God.
We see that God did approve of and did reward Jacob with the promise. (Genesis 28:13-15) In faith, Jacob had sought God’s favor, obtained the Covenant promise, and never sold it. Throughout his life, he loved and worshipped God, and diligently sought to know and to do His will.
Esau, on the contrary, steadily pursued a wayward course. He married heathen wives who were a cause of grief to Isaac and Rebekah (26:34,35). And he hated his brother and determined to slay him.
However, God did decide to teach Jacob lessons about lying. God gave him many hard life experiences where Jacob, himself, became the victim of lies. Jacob suffered and learned the sinfulness of lying.