David's best adviser, Ahithophel, told Absalom to publicly seduce the concubines that David had left to take care of the palace. Because the concubines were the king's property, having sexual relations with a king's concubines implied that Absalom was now the king. This would show the people that the break with David was complete. (See: [[rc://en/ta/man/jit/figs-explicit]])
To show how seriously people took Ahithophel's advice, the author used a simile comparing his advice to God's advice. "Now the advice of Ahithophel that he gave in those days was as if a man heard from the mouth of God himself." (See: [[rc://en/ta/man/jit/figs-simile]])