Gods grace overcomes all of our sin

Ps 143 1 O LORD, hear my prayer, listen to my cry for mercy; in your faithfulness and righteousness come to my relief.2 Do not bring your servant into judgment, for no one living is righteous before you.3 The enemy pursues me, he crushes me to the ground; he makes me dwell in darkness like those long dead.4 So my spirit grows faint within me; my heart within me is dismayed.

5 I remember the days of long ago; I meditate on all your works and consider what your hands have done.6 I spread out my hands to you; my soul thirsts for you like a parched land. "Selah"7 Answer me quickly, O LORD; my spirit fails. Do not hide your face from me or I will be like those who go down to the pit.8 Let the morning bring me word of your unfailing love, for I have put my trust in you. Show me the way I should go, for to you I lift up my soul.9 Rescue me from my enemies, O LORD, for I hide myself in you.10 Teach me to do your will, for you are my God; may your good Spirit lead me on level ground.11 For your name's sake, O LORD, preserve my life; in your righteousness, bring me out of trouble 12 In your unfailing love, silence my enemies; destroy all my foes, for I am your servant.

This Psalm is teaching us that the Holy Spirits work in our salvation is acting on our behalf as an advocate. The Psalmist opens this Psalm with two covenant attributes that he presents as his argument as the basis of the Holy Spirits success in our lives. We are taught that God has promised to deliver us in all of our lives by His faithfulness and righteousness.  The Psalmist knows that Gods saves us according to His unfailing love. Throughout the Psalms when the Psalmist presents his argument to God he argues on the basis of Gods attributes as the way to gain confidence that he will be delivered by God. In this sense the Psalmist is encouraging himself by reminding himself and God of Gods promise to act on behalf of the Psalmist in showing that He is serious about doing as He promised. 

These two attributes provide us with the view the Psalmist has about Gods work in salvation.  God is faithful in that He has completed the work that was necessary to make us acceptable. If you examine this Psalm you will see that the Psalmist stands on Gods love and faithfulness and uses other words that describe his salvation that are interchangeable with Gods love and faithfulness. This is the normal way that the Psalmist approaches God. You will see that sometimes the Psalmist pleads to God in describing his sorrow and sometimes the Psalmist pronounces cursing and blessing and then appeals for God to act on the basis of His unfailing love alone. Appealing to God according to His unfailing love is this application on a much more detailed way in appealing according to the specific promises in the covenant 

He is saying that our salvation is a completed gift that cannot fail.The reason that we cannot fail is because we stand before God as completely righteous. In saying that  "no one living is righteous before you".the Psalmist is that every man is guilty so that when we fail there is no one on the earth that we can point to and "I dont deserve salvation because another person is better than me". using the lowest common denominator to show that God has gone low enough to take care of the most severe suffering that we can go through on this earth. We are always taught that we grow from hearing the bad news. But this is not really the covenant message to us. Rather God lowers Himself to our level as if he were a man judging our success in comparison to other men. Instead of saying that we do not deserve salvation because these other people are not doing a sin and we are...God says that if He were to remember our sin and judge us He would need to judge all those men outside of Jesus ...He would need to judge them first even tho among men our sin may be consider worse. Gods forgiveness is His forgetfulness even if we fail in sinning over and over again. The success of our getting better is that we always receive forgiveness for free. It is so free that even tho we sin we cannot be judged because there is someone that is always farther along than us and worse than us. This is the basis of arguing for the Holy Spirits success in the rest of the Psalm.