King David is a paradigm of doing teshuva. His Teshuva had many parts, both illustrated in the story and explained in Tehilim (especially mizmor 51).
One of the lesser known steps happened when he was running away from Avshalom. When David is on the run from Avshalom, he has the opportunity to take the Aron Hakodesh with him. Instead he sends it back to the city. He explains this to Tzadok:
כה וַיֹּאמֶר הַמֶּלֶךְ לְצָדוֹק, הָשֵׁב אֶת-אֲרוֹן הָאֱלֹהִים הָעִיר: אִם-אֶמְצָא חֵן, בְּעֵינֵי יְהוָה–וֶהֱשִׁבַנִי, וְהִרְאַנִי אֹתוֹ וְאֶת-נָוֵהוּ. כו וְאִם כֹּה יֹאמַר, לֹא חָפַצְתִּי בָּךְ: הִנְנִי–יַעֲשֶׂה-לִּי, כַּאֲשֶׁר טוֹב בְּעֵינָיו.
And the king said to Tzadok, return God’s ark to the city; if I find favor in Hashem’s eyes, He will returns me, and show me it and His place.
And if He says, I don’t desire you, I am ready for Him to do what is good in His eyes.
David explains that he is still distant from God because of his sin, as manifest in his need to run away from Avshalom. Therefore, it would be wrong to take the Ark with Him.
Some points we learn from this.
1. Often we feel that saying sorry is enough. If we apologies and repent then everything is better.
David did not accept this reasoning. he didn’t say that since he did Teshuva, therefore he is close to God, and of course it was accepted. Rather he recognized that in spite of his teshuva, he was still distant, and furthermore, there was no guarantee that God would accept him back. He recognized the extreme evil that he did, and was accepting of the consequences, while hoping to return to his previous closeness to God. We cannot control God by doing Teshuva. While we have confidence that a Baal Teshuva is close to God, Teshuva is not something we can manipulate God through.
We see a similar idea on Rosh hashanah. On the one hand we don’t say Hallel because excessive joy is not appropriate for a day of judgment, awe, and teshuva. On the other hand, there are indications that we as a people have confidence in the outcome of this judgment, for example by dressing up for the occasion. How are these compatible? Our confidence in the judgment comes from taking security in God. Only if we take the judgment seriously, with all of the fear and awe that entails, do we turn to God as a source of trust. We are confident in the outcome, because we trust God, not because the process is fake.
2. He could have taken the Aron with him in order to show the people that God was with Him, instead he showed that the Aron should not be used for human honor. Rather it is his responsibility is to honor God by treating it respectfully. This directly opposes the story at the beginning of Shmuel about the sons of Eli who used the mikdash for their own honor. This also opposes their other sin of viewing the Aron as a magical object of power, bringing it to the war with the Pelishtim. (One recurring theme in the story of David is restoring the proper relationship of the people to the Aron and mikdash).
As a king he recognized his dependency on God, rather then viewing religion as a tool for advancing his interests.