Psalm 51.

 10)Create in me a pure heart, O God,

    and renew a steadfast spirit within me.

11) Do not cast me from your presence
    or take your Holy Spirit from me.

12) Restore to me the joy of your salvation
    and grant me a willing spirit, to sustain me.

Here's a breakdown:

• "Create in me a pure heart, O God, and renew a steadfast spirit within me":

  This is a plea for a complete renewal, both emotionally and spiritually. The psalmist desires a heart free from sin and a spirit that is resolute and unwavering in its commitment to God. A steadfast spirit is needed to persevere through difficult times and to remain faithful to God. 
• "Do not cast me from your presence or take your Holy Spirit from me":

  This expresses the psalmist's deep fear of separation from God's grace and guidance. He acknowledges that sin has caused a separation and prays for God's forgiveness and continued presence. The Holy Spirit is seen as essential for spiritual growth and guidance. 
• "Restore to me the joy of your salvation and grant me a willing spirit, to sustain me":

  The psalmist desires to experience the joy of God's forgiveness and the renewed sense of purpose that comes with a restored relationship. A willing spirit is a spirit that is receptive to God's guidance and desires to serve Him.