11 Now King David was old and far on in years; and though they put covers over him, his body was cold. 2 So his servants said to him, Let search be made for a young virgin for my lord the king, to take care of him and be waiting on him; and you may take her in your arms, and so my lord the king will be warm. 3 So after searching through all the land of Israel for a fair young girl, they saw Abishag the Shunammite, and took her to the king. 4 Now she was very beautiful; and she took care of the king, waiting on him at all times; but the king had no connection with her.
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.