John Calvin Commentary Genesis 27:19

"And Jacob said unto his father, I am Esau thy first-born; I have done according as thou badest me: arise, I pray thee, sit and eat of my venison, that thy soul may bless me." — Genesis 27:19 (ASV)

And Jacob said unto his father, I am Esau. At first Jacob was timid and anxious; now, having dismissed his fear, he confidently and audaciously lies. From this example, we are taught that when anyone has transgressed the proper bounds of duty, he soon allows himself unrestrained license.

Therefore, there is nothing better than for each to keep himself within the limits divinely prescribed to him, lest by attempting more than is lawful, he should open the door to Satan. I have previously shown how far his seeking the blessing by fraud, and insinuating himself into the possession of it by falsehood, was contrary to faith.

Yet this particular fault and divergence from the right path did not prevent the faith which had been produced by the oracle from somehow holding its course. In excusing the quickness of his return by saying that the venison was brought to him by God, he speaks in accordance with the rule of piety; he sins, however, in mixing the sacred name of God with his own falsehoods.

Thus, when there is a departure from truth, the reverence which is apparently shown to God is nothing other than a profanation of his glory. It was right that the successful outcome of his hunting should be ascribed to the providence of God, lest we should imagine that any good thing was the result of chance; but when Jacob pretended that God was the author of a benefit which had not been granted to himself, and that, moreover, as a cloak for his deception, his fault was not free from perjury.