“But Amnon had a friend whose name was Jonadab the son of Shimeah, David’s brother. Now Jonadab was a very crafty man” (2 Samuel 13:3 NKJV).

Who was Jonadab?
Jonadab was the son of Jesse’s third son, David’s brother, Shimeah. He was David’s nephew and a supposed “friend” to David’s firstborn son, Amnon. Yet, on this occasion his true identity was revealed, for as the serpent in the garden of Eden was described as “crafty” (Gen. 3:1), so was he. And as the serpent tempted Adam, he tempted Amnon, advising him of a way to obtain the forbidden fruit of his sister, Tamar. His subtle strategy even involved David, so that his involvement would produce the desired result.
So, Amnon followed Jonadab’s advice and raped his his half-sister, Tamar, the full-sister of Absalom, who hated his brother from that day. And two years later, Absalom conspired to have Amnon killed.
Now adultery and murder, which had been David’s sins, had been found in David’s sons. And where was Jonadab when the news of Absalom’s revenge was heard in the royal court? He was at the king’s side, advising him not to worry that all his sons were dead at the hands of Absalom, but only Ammon. How did Jonadab know this? He must have been in on Absalom’s secret. Perhaps he had been Absalom’s advisor too.
Who was Jonadab? He was the serpent in David’s family. The crafty advisor that led them to follow their fleshly desires.
The peace in David’s life was ended. From that day forward, his life was followed with one trouble after another. Surely he could trace his children’s sins to his own, which must have made the pain of it all the more. His sin had left open the door of his house, allowing a serpent to crawl inside and find a mouthpiece in David’s nephew, Jonadab.