Genesis 4:9
And the LORD said unto Cain, Where is Abel thy brother? And he said, I know not: Am I my brother's keeper?
And the LORD said unto Cain, Where is Abel thy brother?.... Perhaps this was said to him the next time he came to offer, he not being with him: this question is put, not as being ignorant where he was, but in order to bring Cain to a conviction and confession of his sin, to touch his conscience with it, and fill it with remorse for it; and, for the aggravation of it, observes the relation of Abel to him, his brother:
And he said, I know not; which was a downright lie; for he must know where he had left him or laid him: this shows him to be under the influence of Satan, who was a liar, and the father of lies, as well as a murderer from the beginning; and that he was so blinded by him, as to forget whom he was speaking to; that he was the omniscient God, and knew the wickedness he had done, and the falsehood he now delivered, and was capable of confronting him with both, and of inflicting just punishment on him.
Am I my brother's keeper? which was very saucily and impudently spoken: it is not only put by way of interrogation, but of admiration, as Jarchi observes, as wondering at it, that God should put such a question to him, since he knew he had not the charge of his brother, and his brother was at age to take care of himself; and if not, it rather belonged to God and his providence to take care of him, and not to him: so hardened was he in his iniquity, he had stretched out his hand against his brother, and now he stretched it out against God, and ran upon him, even on the thick bosses of his buckler.