Forgiveness of our past sins is our very first and our constant need. The guilt of our sins could not be removed by God by any other way than by the payment of the full penalty for our sins. "Without the shedding of blood, there is no forgiveness" (Hebrews 9:22).
When Christ shed His blood on the cross of Calvary, it purchased the pardon of every sin ever committed by anyone. But that pardon becomes ours only when we receive it. Through Christ's blood we now have the forgiveness of all our sins, if we sincerely turn from our sins (repent), trust in Him, and receive the forgiveness that he offers.
The blood of Christ also justifies us (Romans 5:9). This is more than just being forgiven. It is being declared righteous, just as though we had never sinned in our entire lives. God's promise is that "He will not remember our sins any more" (Hebrews 8:12). That means that He looks at us just as if we had never sinned. That is the meaning of being justified. Such is the power of Christ's blood. Many believers live in perpetual condemnation concerning their past lives, because Satan has hid from them the fact that God has justified them through Christ's blood.
Through the blood of Christ we are redeemed (1 Peter 1:18). That means that we have been purchased from the slave-market of sin. The blood that Christ shed on Calvary was the ransom price that He paid to meet the demands of God's holy Law, so that we might be free, and not slaves any longer. We are born to be free. We need not be slaves any longer to Satan or men or to condemnation or guilt or fear or sin.
Through the blood of Christ, we are also brought into God's presence (Ephesians 2:13). God dwells in light that no man can approach. The only way to come into His presence is through the blood - till the end of our lives. However saintly we may become, our access to God's presence will always be through the blood of Christ. Many believers tend to forget this, once they get victory over conscious sin, and end up as Pharisees.
Through the blood shed on Calvary's cross, Christ has made peace with God (Colossians 1:20). God is not an Enemy to us now. This is a fact that needs to be established in our minds firmly. Many believers live with the feeling that God is constantly unhappy with them and is always frowning at them. This is Satan's lie, designed to bring believers into condemnation and to hinder their spiritual growth. Through the blood of Christ, we have become friends of God. Unless we believe this, we will never make any spiritual progress.
The blood of Christ also cleanses us continually from all sin, when we walk in the light (1 John 1:7). To walk in the light is to walk in victory over all conscious sin. But even when we live in victory over conscious sin, there is still plenty of unconscious sin in all of us. That is why John goes on to say, "If we say we have no sin, we deceive ourselves" (verse 8).
It is not because we have a flesh, that we sin unconsciously, but because we have lived in conscious selfishness for many years, both prior to, and subsequent to our conversion. Jesus had the same flesh as we have. But because He never lived in selfishness at any time, He never sinned unconsciously even once. There was no sin at all in Him (1 John 3:5).
Our unconscious sins (which constitute perhaps about 90% of our total sins initially) are continually cleansed by Christ's blood, so that we can have constant, and unbroken fellowship with the Father.
Through the blood of Christ, we also overcome Satan and his accusations (Revelation 12:11). Satan accuses us to God, to other men and to ourselves constantly. But we can overcome his accusations by confessing ("the word of our testimony") that we have been forgiven, justified, redeemed, brought near to God, brought to peace with God and cleansed by the blood of Christ. Satan can have no power over us any longer.
We need the blood of Christ to cleanse us DAILY, for all of us sin unconsciously daily, and many believers sin consciously too.