God requires that his justice be satisfied. Therefore the claims of his justice must be paid in full, either by ourselves or another. This is the message of the Bible: we sinned but Christ fully paid the claims of God's justice. He will justify many. He will bear their iniquities. Isaiah is talking about Jesus. To satisfy God’s justice, Jesus pays for our sins in full.

In v20, Paul gives the clarification the Jewish people needed to hear: no one can be justified by upkeeping

Because your sin has been fully atoned (paid) for, you are now completely justified before God. continue, and you do need to continue to confess and repent from your ongoing sin, be assured that your justification

It is God who justifies. 34  Who then is the one who condemns? No one.

Yet they do not count toward our justification— for by faith in Christ we are justified, even before

Yet they do not count toward our justification— for by faith in Christ we are justified, even before

Therefore, far from making people cold toward living in a pious and holy way, this justifying faith,

In other words, God decreed  to grant them true faith in Christ, to justify them,  to sanctify them, 

Therefore, far from making people cold toward living in a pious and holy way, this justifying faith,

of his Son’s costly death  should work itself out in all the elect,  in order that God might grant justifying