"Have mercy upon me, O God,
According to Your lovingkindness;
According to the multitude of Your tender mercies,
Blot out my transgressions.
Wash me thoroughly from my iniquity,
And cleanse me from my sin.
...
Behold, I was brought forth in iniquity,
And in sin my mother conceived me.
Behold, You desire truth in the inward parts,
And in the hidden part You will make me to know wisdom.
...
Create in me a clean heart, O God,
And renew a steadfast spirit within me.
Do not cast me away from Your presence,
And do not take Your Holy Spirit from me.
Restore to me the joy of Your salvation,
And uphold me by Your generous Spirit.
Then I will teach transgressors Your ways,
And sinners shall be converted to You.
...
For You do not desire sacrifice, or else I would give it;
You do not delight in burnt offering.
The sacrifices of God are a broken spirit,
A broken and a contrite heart—
This is a prayer for the promise which is to be manifested in Jesus, here we see an understanding from David of this promise. First, It was according to His loving kindness, grace. Jesus became the lamb of God, once and for all we are cleansed. He became our high priest, an earthly high priest had to sacrifice continually for sin. God desires men after His own heart, truth in the inward parts. David knew this, he asks for such a heart. He sees that God doesn't desire sacrifice but truth in the inward being. This is the foundation of the new covenant, one established within us, as truth is established on our hearts and put in out minds, it is what comes from the heart."I will give you a new heart, and a new spirit I will put within you. And I will remove the heart of stone from your flesh and give you a heart of flesh."2
A new covenant Jesus gives, a new heart, a new spirit, a new creation in our inner being that delights in the laws of God. This is the truth God desires, from the inward parts. Through this new covenant established within us, we are given a steadfast heart with bold access to the throne of God. We are sealed with the Holy Spirit that God doesn't take away, we are eternally adopted, by a good good Father. His Spirit is a guarantee of the inheritance of the promise.3 "Now He who establishes us with you in Christ and anointed us is God, who also sealed us and gave us the Spirit in our hearts as a pledge."4 This new covenant is being born from above, in our inner being. "Truly, truly, I say to you, if not anyone is born from above he is not able to see the kingdom of God."3 This new covenant is "written not with ink but with the Spirit of the living God, not on tablets of stone but on tablets of human hearts."5