In II Samuel 16, David is on the run from Absalom. A man approaches David during his flight: Ziba, the servant of Mephibosheth. Mephibosheth is the paraplegic son of Jonathan whom David welcomed into the palace. Ziba tells David that Mephibosheth stayed behind in Jerusalem to take back the throne for the Saulites, in the midst of the turmoil of Absalom's revolt. While commentators have argued that Ziba's claim was implausible, since a paraplegic couldn't take back the throne, A.A. Anderson points out that Mephibosheth had a son in his 20s (II Samuel 4:4; 9:12), so he'd have help if he wanted to become king.
Because Ziba and his servants had charge over Mephibosheth's produce (II Samuel 9:10), Ziba had access to a lot of food, which he brought to King David to sustain him and his men. When Ziba tells David about Mephibosheth's act of treason, David gives Ziba all of Mephibosheth's land, which at one time was Saul's estate.
In II Samuel 19, after Absalom has died, Mephibosheth comes to David, who is heading back to Judah to resume his kingship. According to the narrative, Mephibosheth hadn't taken care of his feet, washed his clothes, or trimmed his beard since David's flight from Jerusalem. Mephibosheth tells David that Ziba had lied about him trying to take the throne for the Saulites. David then orders Mephibosheth to divide his land with Ziba. But Mephibosheth lets Ziba have all of the land, for he's just happy that David has returned safely.
I've not yet come to II Samuel 19 for my weekly quiet time, so I'm not entirely sure why David divided the land between Mephibosheth and Ziba, rather than giving all of it back to Mephibosheth. But my hunch is that David wasn't sure whom to believe: Ziba, with his claim that Mephibosheth tried to take the throne, or Mephibosheth, who said Ziba was lying.
I tend to believe Mephibosheth. The reasons are (1.) that the narrative indicates Mephibosheth was genuinely sad when David fled from Jerusalem, showing he loved David, and (2.) Mephibosheth let Ziba have all of the land, which shows he wasn't selfish.
At the same time, one could argue that Ziba had qualities as well. Ziba approaches David and offers him support, when there's a solid possibility that Absalom can take the throne. That's pretty gutsy! Of course, things weren't totally in Absalom's favor at the time Ziba came to David, for later, in v 21, Ahithophel advises Absalom to sleep with David's concubines so as to encourage his supporters. According to Rashi, Absalom's supporters were afraid that Absalom would reconcile with David and leave them hanging, so they weren't completely gun-ho about Absalom. "What if Absalom and David make up, and David comes after us?," they feared. But, when Absalom slept with David's concubines in public, Absalom officially made a claim to David's throne and permanently alienated David, thereby encouraging his (Absalom's) supporters that he meant business and had no intention to reconcile with his father. So Ziba approached David when Absalom's supporters weren't entirely certain about their stance, since Absalom hadn't yet made his bold move with David's concubines.
Still, it was gutsy for Ziba to approach David and his handful of men, since it wasn't yet certain that David would regain the throne. And this is the point I want to make: I think that Ziba believed God was on David's side and would restore David to the throne. Ziba saw God do this for David before, when God took the throne from Ziba's master, Saul, and gave it to David. So Ziba had some sort of faith.
But Ziba's belief in God didn't result in moral character, for he was selfish and greedy. He lied about his master to get Mephibosheth's property for himself. Belief in God doesn't always make a person moral. We may approach God solely to get goodies for ourselves. Granted, it's not wrong to believe that God wants to bless us, for David himself in II Samuel 16:12 hopes that God will take notice of his punishment or his eyes (perhaps the tears therein), take pity, and return good to him, while Shimei is cursing David and pelting him with rocks. Many suggest that God allowed Shimei to curse David so David would have an opportunity to look to God as his deliverer and vindicator, rather than taking vengeance on Shimei himself.
I don't think that self-interest should be removed from the religious life, for God wants to bless us and takes notice of the good things that we do, hopefully rewarding the good and punishing the bad. But the religious life should not be solely about "get, get, get," as if it's a sort of magic. It should also be about being good people, who love God and their neighbors. Ziba believed in God, and he thought that God was on David's side, but that didn't lead him to have a good character.
Mephibosheth, by contrast, was loyal to David. He was grateful that David had shown him such compassion when he (Mephibosheth) was a paraplegic from a dejected and forsaken royal house. Mephibosheth should have been history, but David gave him a future. So Mephibosheth loved David and was torn apart inside when David had to flee Jerusalem. When David returned after his victory over Absalom, Mephibosheth didn't care so much about Ziba taking his land; Mephibosheth was worried that David thought badly of him on account of Ziba's slander. He was perfectly willing to let Ziba keep the land, as long as David could continue to be king, and Mephibosheth could be in a relationship with him (okay, the last part isn't explicitly in the text).
Mephibosheth is a model of the Christian life: being grateful to God on account of his love and mercy, loving God and desiring his rule on earth, being so satisfied in God that material things and personal resentments don't matter so much. Mephibosheth's attitude was like that of the Psalmist in Psalm 84:10: "I would rather be a doorkeeper in the house of my God than live in the tents of wickedness" (NRSV).