throwing yourself on the mercy of God

King David knew that before the judgment seat of God he didn't have any hope trusting in his own righteousness. What he needed was to experience the mercy of God in forgiveness:

"O LORD, hear my prayer,
listen to my cry for mercy;
in your faithfulness
and righteousness come to my relief.
Do not bring your servant into judgment,
for no one living is righteous before you."
Psalm 143:1-2

The same has been true for everyone for all time. The only hope each one of us has on the day of judgment is to have received forgiveness from God. The great news is that God does hear our cry for mercy, he is willing to forgive. As the Apostle Peter says,

“Repent and be baptized, every one of you, in the name of Jesus Christ for the forgiveness of your sins. And you will receive the gift of the Holy Spirit. The promise is for you and your children and for all who are far off — for all whom the Lord our God will call.” Acts 2:38-39.