No matter how long you've walked with God, there is that remnant nub of works-righteousness hiding in our reborn hearts.
"How can I expect God to bless my day when I so recently sinned against Him?"
"I need to read a lot of scripture and bring dinner to a needy family before I will feel confident to ask God for anything."
Imagine how David must have felt when he had to flee Jerusalem and the palace because of reports that his rebel son, Absolom, was closing in upon him, stealing the hearts of Israel and seizing the palace.
Samuel records him trudging up Mt. Olivet with his head slumped and tears forcing their way down his rugged cheeks. How dreadfully he had sinned with Bathsheba, and how miserably he multiplied his guilt by planning the death of her husband. Though David repented, and though Nathan, the prophet of God, told him his sin was forgiven, there were consequences with which David would be haunted. One of those consequences was trouble in his own household. Now it was coming in more dramatic form than David could have guessed.
Shimei threw gravel at David and cursed him from the hill top as David was making his way out of town. David restrained his faithful companion from wreaking vengeance, saying, "Let him alone, and let him curse for the Lord has told him."
But David was grace-minded. He knew God as few people do. Later God calls him the man after "my own heart". When God forgives sin, He actually puts it from us as far as the east is from the west. A forgiven sinner is always a recipient of God's blessings. He always enjoys direct communication to God.
Fast forward to Psalm 3. This Psalm specifically identifies itself as being composed on the occasion of David's flight from Absolom. He bemoans the fact that his enemies are multiplying, and they are saying that God will not help him. It was tempting to believe those taunts because David was forever aware of his sin.
But David knows that God is a friend for forgiven sinners, and He is never a fickle friend. He says, "But You, O Lord, are a shield about me, my glory and the One who lifts my head." Leaving Zion, David's head was bowed, but God lifted that dear head in due time.
"Salvation belongs to the Lord" David shouts at the crescendo of the Psalm. Only one who is grace-minded can do that in such circumstances. Sin disqualifies us from the favor of God. Our shame would take us to the mat and hold us there except for one thing: Salvation belongs to the Lord. Once He has declared His love for you, there is no way He will change His mind. After all, He knows the end from the beginning so what could possibly make Him change His mind? Since salvation is dependent upon what God has done, rather than upon anything you have done, it is secure for now and for eternity.