11 Now King David was old and advanced in years. And although they covered him with clothes, he could not get warm. 2 Therefore his servants said to him, "Let a young woman be sought for my lord the king, and let her wait on the king and be in his service. Let her lie in your arms,[1] that my lord the king may be warm." 3 So they sought for a beautiful young woman throughout all the territory of Israel, and found Abishag the Shunammite, and brought her to the king. 4 The young woman was very beautiful, and she was of service to the king and attended to him, but the king knew her not.
Matthew Henry's Commentary on 1 Kings 1:1-4
Commentary on 1 Kings 1:1-4
(Read 1 Kings 1:1-4)
We have David sinking under infirmities. He was chastised for his recent sins, and felt the effects of his former toils and hardships.