Let me complete the question, “Should Christians ask God for forgiveness knowing that all their sins, past, present and future, have already been forgiven by God when they were justified by their faith in Christ?”
Justification by Faith
The Bible teaches that when we put our faith in Christ God justifies us and we are declared not guilty before him. All our sin is counted to Jesus – who died for our sins in our stead – who thereby bore God’s punishment that should have been ours. All Jesus’ right standing before God is then counted to us. We are justified before God, counted righteous in his sight, and our sin (all of it) forgiven. As Paul says in Romans 8 there is therefore no condemnation for those who are in Christ (v1) and nothing can separate us from his love (v38-39) – ever. God himself gave himself to save us from himself.
The thinking in some circles is that we, as Christians, shouldn’t ask God for forgiveness. We can thank God for his past forgiveness and turn again from sin, but to ask God for what he has already granted is illogical.
In Psalm 51 King David typifies how Christians should respond to sin. David does not become a believer in this Psalm, he is already a believer. The Psalm exemplifies the response of the believer confronted with his own sin and fallenness.
Impress your friends
The heading or superscription gives us the historical background to Psalm 51, “For the director of music. A psalm of David. When the prophet Nathan came to him after David had committed adultery with Bathsheba.” All the heading in the Psalms are part of the original Hebrew text and therefore part of inspired Scripture. If you want to impress you Christian friends you should always read the heading. (The section headings found else where in the Bible are not part of the original Hebrew and Greek manuscripts and should be regarded as helpful, but not inspired. The section heading were added by translators to aid our reading.)
David was a believer. But he had just committed adultery and murder. How does he respond? David confesses his sin and asks God for forgiveness. David cries out, “Have mercy on me, O God, according to your unfailing love; according to your great compassion blot out my transgressions. Wash away all my iniquity and cleanse me from my sin.” (v1-2) No excuses. No blame-shifting. No pretence. Only honest confession before God and crying out for God’s forgiveness.
What David says in verse 4 is very interesting. He says, “Against you, you only, have I sinned and done what is evil in your sight…” Surely David sinned against Bathsheba by taking advantage of her; surely David sinned against Uriah by sleeping with his wife and killing him; surely David sinned against God’s people by his lack of integrity? What David realised is that when we sin, we do sin against others, but first and fore mostly we sin against God who is holy and good. And because our sin is ultimately against God, we can only go to God for forgiveness.
What David asks for seems an impossibility. In v10 David asks for a pure heart. How can an adulterer, a murderer and an evil schemer acquire a pure heart? v7 is the clue. David asks for cleansing with hyssop. The hyssop plant was used by priests when making sacrifices and purification rituals. The hyssop was normally dipped in a dead animal’s blood. The big lesson for the Israelites was that there is no cleansing without the shedding of blood. No forgiveness without death. Instead of you dying, the animal dies. Indeed, the whole sacrificial system in the Old Testament points us to the death of Jesus, the only death that can truly take away sin and make us acceptable to God. Only Jesus’ death can provide us with “pure hearts” (v10).
The Lord’s Prayer
David, a forgiven person, asks for forgiveness. This should not surprise us as this is consistent with how Jesus taught his followers to pray. For example, Jesus promised to take care of all the needs of his disciples (Matthew 6:33), yet he said they should pray, “Give us today our daily bread” .
Similarly, God declares us righteous and forgives all ours sins when we become Christians, yet Jesus taught his disciples to pray, “Forgive us our debts as we also have forgiven our debtors”. God has forgiven, and we continue to appropriate that forgiveness.
The Prayer Book
The Prayer Book of our denomination is very helpful in this regard. Whenever we as a church come together for corporate worship, the Prayer Book has us pray together – as a congregation – a prayer of confession that goes something like this:
Almighty God, heavenly Father, we confess that we have failed you in our thoughts and words and deeds. Because we are sinners by nature we have strayed from your ways and not only have we done wrong but we have failed to do right. Lord, you alone can forgive sin, have mercy on us, pardon our sins and help us to serve you not only with our lips, but with our lives, through Jesus Christ our Lord. Amen.
Fellowship with God
In v12 David does ask for salvation, but the God would “restore to me the joy of your salvation”. Our sin as Christians does not destroy our right standing before God, but our joy in God. Our daily fellowship with God is tarnished, our prayer life is hampered, our “bones are crushed” (v8), and our praise is hollow. Like David we need to come honestly before God and cry out, “Wash away all my iniquity and cleanse me from my sin.”