Keil & Delitzsch

The king understood the meaning of the words. He was agitated, and went up to the balcony of the gate (the room above the entrance) and wept, and said, walking about, "My son Absalom, my son, my son Absalom! Oh that I had died for thee, Absalom, my son, my son!" To understand this passionate utterance of anguish, we must bear in mind not only the excessive tenderness, or rather weakness, of David's paternal affection towards his son, but also his anger that Joab and his generals should have paid so little regard to his command to deal gently with Absalom. With the king's excitable temperament, this entirely prevented him from taking a just and correct view of the crime of his rebel son, which merited death, and of the penal justice of God which had been manifested in his destruction.