Why did David decide to return the Aron?
Malbim #1: No matter what will happen to me, this is proper! If Hashem desires me, He will return me to its place. And if not - I cannot bring the Aron where He does not want it!
Malbim #2: According to Chazal, he was unsure if the Urim v'Tumim did not answer him due to Evyasar, or because he removed the Aron from its place. Therefore, he now returned the Aron and asked via Tzadok.
What is the meaning of "ve'Heshivani v'Hir'ani Oso v'Es Navehu"?
Radak: If Hashem will return to love and desire me 1 [and He will show me] the house where the Aron was. Now, due to punishment for my sin, He is distanced from me, like one who hides his eyes from his enemy, and does not see him.
Radak citing Targum Yonasan: Va'Yachaziani Kadamohi va'Eflach Kadamohi b'Veis Mikdeshei 2 .
Malbim: David now explains what his question to the Urim v'Tumim was. If Hashem desires me, He will answer that I will return to see the Aron and His abode.
I.e. He will show me that He desires me again. (PF)
Yayin ha'Tov: He will find me worthy in front of Him, and I will serve Him in [his] Beis ha'Mikdash. (Nasan already told David that he will not build it! Perhaps he means that in place where the Mikdash will be built, or refers to Techiyas ha'Mesim. - PF)