David's sin was the issue of his indulging of the lust of the eyes and the lust of the flesh (vv. 2b-3).
David committed a willful adultery by robbery, abusing the power of his kingship (vv. 4-5). This was a real insult to God. David's great sin nearly annulled all his attainments from the past.
After committing a willful act of adultery, David pretended to cover his evil deed (vv. 6-13). Eventually, God exposed him.
David murdered Uriah, his faithful servant, by a conspiracy with Joab (vv. 14-25).
In a letter, David instructed Joab to put Uriah in the forefront of the hardest battle and then withdraw from him so he might be stricken down to death (vv. 14-15). By giving such a word to Joab concerning Uriah, David abused his kingship. Joab did what David commanded, and Uriah was killed.
Not only was Uriah slain, but also "some of the people, some of the servants of David, fell" (v. 17b). This indicates that David murdered Uriah even at the sacrifice of the life of some of the servants of David.
Joab surely realized that he was involved in a conspiracy to carry out a great sin, and his conscience must have condemned him. David comforted and encouraged Joab, the one who carried out the conspiracy, by saying, "Do not let this matter displease you, for the sword devours one as well as another. Strengthen your fighting against the city and overthrow it" (v. 25). What a terrible thing for David to say! Uriah was not merely devoured by the sword—he was actually murdered by David so that he could take Uriah's wife.
David's behavior here was utterly different from that of Joseph and Boaz. Joseph was tempted, but he ran and escaped from adultery (Gen. 39). Boaz, David's forefather, also kept himself clean from the indulgence of the flesh of sin (Ruth 3). This purity kept Boaz in the line of the genealogy of Christ. David, however, willingly committed adultery. By his one sin David broke the last five of the Ten Commandments (Exo. 20:13-17).
Before David was crowned and enthroned, he already had a number of wives. Second Samuel 5:13 says that he took more concubines and wives. David was perfect in every way, but he was weak in the matter of the indulgence of the lust of the flesh. The lust of the flesh is like a wild horse. To subdue this lust, we must hold the bridle very tightly. In this matter David was loose, and he sacrificed his high attainment in the pursuit of God. David was a great "diamond," but his indulgence in lust was a black, foreign particle in this diamond. Even though he was a person of high attainment in his spiritual pursuit, he was still able to commit such a great sin.