Sin is the biggest form of frustration for Christians just as it was for the writer of this psalm. He wrote, “From the depths of despair, O Lord, I call for Your help. Hear my cry, O Lord. Pay attention to my prayer.”
Why did he feel this way? He must have thought he was the only person who felt this guilt. But the truth is all believers have felt the guilt. David knew when he sinned with Bathsheba that he was guilty, and when he found out she was pregnant, he tried to cover it up by bringing her husband home from the battlefield. When that didn’t work, David had her husband placed in a position at the battlefield where he would be killed.
C. S. Lewis wrote a book called The Screwtape Letters. In that book, Lewis imagines Satan writes to his nephew, Screwtape, hints on how to get a Christian to sin so he can accuse him with guilt trips. Scripture gives us an illustration of this in Zechariah 3. Zechariah wrote, “Then the angel showed me Jeshua the high priest standing before the Angel of the Lord. The Accuser, Satan, was there at the Angel’s right hand, making accusations against Jeshua. And the Lord said to Satan, ‘I, the Lord, reject your accusations, Satan’.”
In Scripture, references to the Angel of the Lord appear to be a reference to the pre-incarnation appearance of the Lord Jesus Christ, and it appears it was the Angel of the Lord who rebuked Satan. But Satan is always accusing us because he doesn’t want us to share our faith with others.
In the case of this psalm writer, he was limited in his understanding because of the religious system in Israel. Sacrifices for sin had to be made, but it was only once a year on the Day of Atonement that the high priest could enter the Holy of Holies to sprinkle blood on the Mercy Seat to atone for sin. So each year of sins were atoned for on one specific day.
However, when Christ died on the cross and rose again, He presented His blood to God the Father. Talking about Jesus, Paul writes, “Therefore He is able, once and forever, to save those who come to God through Him. He lives forever to intercede with God on our behalf.” Heb. 7:25