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 maiden be sought for my lord the king, and let her wait upon the king, and be his nurse; let her lie in your bosom, that my lord the king may be warm." 3 So they sought for a beautiful maiden throughout all the territory of Israel, and found Ab'ishag the Shu'nammite, and brought her to the king. 4 The maiden was very beautiful; and she became the king's nurse and ministered 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.