Let's take a closer look at the story in First Kings Chapter One:
1Now king David was old and stricken in years; and they covered him with clothes, but he gat no heat. 2Wherefore his servants said unto him, Let there be sought for my lord the king a young virgin: and let her stand before the king, and let her cherish him, and let her lie in thy bosom, that my lord the king may get heat. 3So they sought for a fair damsel throughout all the coasts of Israel, and found Abishag a Shunammite, and brought her to the king. 4And the damsel was very fair, and cherished the king, and ministered to him: but the king knew her not." (1 Kings 1: 1-4)
When Adam sinned against God, he saw that he was naked, both he and his wife.
Their response: put on clothes of their own making:
"6And when the woman saw that the tree was good for food, and that it was pleasant to the eyes, and a tree to be desired to make one wise, she took of the fruit thereof, and did eat, and gave also unto her husband with her; and he did eat. 7And the eyes of them both were opened, and they knew that they were naked; and they sewed fig leaves together, and made themselves aprons." (Genesis 3: 6-7)
There is no clothing of our own making which can make us good before God.
We need God to provide the covering for us. God did that for the first man and woman:
"21Unto Adam also and to his wife did the LORD God make coats of skins, and clothed them." (Genesis 3: 21)
Throughout the Old Testament, a promise of a new coat, a robe of righteousness is manifested to us:
"I put on righteousness, and it clothed me: my judgment was as a robe and a diadem." (Job 29: 14)
"I will greatly rejoice in the LORD, my soul shall be joyful in my God; for he hath clothed me with the garments of salvation, he hath covered me with the robe of righteousness, as a bridegroom decketh himself with ornaments, and as a bride adorneth herself with her jewels." (Isaiah 61: 10)
"Salvation" is Jesus! He is our bridegroom, and we in the Church are His bride!
"Who is this that cometh from Edom, with dyed garments from Bozrah? this that is glorious in his apparel, travelling in the greatness of his strength? I that speak in righteousness, mighty to save." (Isaiah 63: 1)
"Mighty to save" - that's Jesus, everyone!
Even in Zechariah, righteousness is pictured a robe which we receive, not something that we earn or do on our own:
"1And he shewed me Joshua the high priest standing before the angel of the LORD, and Satan standing at his right hand to resist him. 2And the LORD said unto Satan, The LORD rebuke thee, O Satan; even the LORD that hath chosen Jerusalem rebuke thee: is not this a brand plucked out of the fire? 3Now Joshua was clothed with filthy garments, and stood before the angel. 4And he answered and spake unto those that stood before him, saying, Take away the filthy garments from him. And unto him he said, Behold, I have caused thine iniquity to pass from thee, and I will clothe thee with change of raiment. 5And I said, Let them set a fair mitre upon his head. So they set a fair mitre upon his head, and clothed him with garments. And the angel of the LORD stood by." (Zechariah 3: 1-5)
We have a Joshua today -- Jesus, who is our high priest:
"Whither the forerunner is for us entered, even Jesus, made an high priest for ever after the order of Melchisedec." (Hebrews 6: 20)
He is our priest forever, seated at the right hand of the Father:
"Who is he that condemneth? It is Christ that died, yea rather, that is risen again, who is even at the right hand of God, who also maketh intercession for us." (Romans 8: 34)
So, David needs warmth to cover himself. His servants decided to bring to him a young virgin to care for him and warm him.
Now, David did not make this decision, but his servants made the decision to bring to him a young virgin named Abishag, "Father or Source of Error."
This is neither wise nor good. This is sin, simple as that. Yet where sin increased, Grace did superabound.