Restore unto me the joy of thy salvation; and uphold me with thy free spirit. Restore unto me the joy of thy salvation - This is an awful prayer. And why? Because it shows he once Had the joy of God's salvation; and had Lost it by sin!
Uphold me with thy free spirit - Prop me up; support me with a princely spirit, one that will not stoop to a mean or base act. See on Psalms 51:10 (note).