[To Saul:] But now your kingdom shall not continue. The LORD has sought out a man after his own heart, and the LORD has commanded him to be prince over his people, because you have not kept what the LORD commanded you." (1 Samuel 13:14 ESV)
Therefore you are great, O LORD God. For there is none like you, and there is no God besides you, according to all that we have heard with our ears. (2 Samuel 7:22 ESV)
So David reigned over all Israel. And David administered justice and equity to all his people. (2 Samuel 8:15 ESV)
Why have you despised the word of the LORD, to do what is evil in his sight? You have struck down Uriah the Hittite with the sword and have taken his wife to be your wife and have killed him with the sword of the Ammonites. (2 Samuel 12:9 ESV)
King Saul lost his kingdom because he didn't do what the Lord commanded. The Lord had instead sought a man who was after His own heart. Finally on the throne, David praised God for the marvelous things He had done in his life. At some point, though, his heart must have begun wandering.
For further study:
Saul lost his kingdom because he didn't follow God's commands. Why do you think David was not punished in the same way?
As you look at the above verses, you may find it hard to believe they all pertain to the same man. How can someone called a man after God's own heart drift so far from that same God that he would sin so grievously? He coveted his neighbor's wife, committed adultery with her, and lied about it with an attempt to cover it up by arranging for the murder of her husband. He was so blind to the sin that he didn't even realize he'd done something wrong until Nathan the prophet told him (See 2 Samuel 12:1-7).
Something like this doesn't just happen overnight. The drift--the slippery slope, if you will--comes long before such a fall as this. It happens in the heart, that within us which is able to deceive unlike any other (Jeremiah 17:9). Therefore, we must be careful to guard our hearts. We must pray regularly for God to search our hearts and try our thoughts to see if there is grievousness in them and to lead us in the way everlasting (from Psalm 139, before David became king over all Israel).
There is one more vital Scripture for us to see. It is one of utter brokenness over sin.
To the choirmaster. A Psalm of David, when Nathan the prophet went to him, after he had gone in to Bathsheba. Have mercy on me, O God, according to your steadfast love; according to your abundant mercy blot out my transgressions. Wash me thoroughly from my iniquity, and cleanse me from my sin! For I know my transgressions, and my sin is ever before me. Against you, you only, have I sinned and done what is evil in your sight, so that you may be justified in your words and blameless in your judgment. (Psalms 51:1-4 ESV)
Are you so far in sin you don't even know it? Maybe your heart has deceived you. If it has, you may not even know the answer is "yes." Take the time right now to pray that God would reveal to you any error in your ways. Be ready for the truth, no matter how ugly it is! . . .Because when you have confessed and repented, you will feel more free than you have in a long, long time. That's the freedom that Jesus brings! Remember it?
So maybe you're not in sin on a regular basis, but perhaps there is at least one area of obedience where you are lacking. Reading your Bible regularly? Praying? Ridding your surroundings of things that disgrace the Lord? What about following through on something God has shown you, but you just keep allowing to slip by? In your quiet time today, begin to seek God's counsel on this and watch how He works. You might also enjoy my friend Jé's convicting article on seeking God first.
Glorify God for the things He reveals!