So what you are saying is; We need Jesus to forgive us our PAST sins that we did prior to repentance?
The purpose of the death of Christ is to purge the conscience of dead works. Even a repentant sinner has a consciousness of their past sin which they cannot, of themselves, remove. Hence a return to obedience can in no way remit past sins.
Heb 9:14 How much more shall the blood of Christ, who through the eternal Spirit offered himself without spot to God, purge your conscience from dead works to serve the living God?
Heb 9:15 And for this cause he is the mediator of the new testament, that by means of death, for the redemption of the transgressions that were under the first testament, they which are called might receive the promise of eternal inheritance.
God is willing to forgive past sin on the condition of repentance and faith...
Pro 28:13 He that covereth his sins shall not prosper: but whoso confesseth and forsaketh them shall have mercy.
Yet the problem that remains is the conscience of the sinner. How can one whom is guilty stand before God in good conscience? The answer is, only through the blood.
The blood is not magical in anyway. God simply chose blood as the means of establishing a covenant...
Heb 9:16 For where a testament is, there must also of necessity be the death of the testator.
Heb 9:17 For a testament is of force after men are dead: otherwise it is of no strength at all while the testator liveth.
Heb 9:18 Whereupon neither the first testament was dedicated without blood.
It is through the sacrifice of Christ that God expresses the true knowledge of righteousness to mankind. We see this alluded to in Isaiah...
Isa 53:11 He shall see of the travail of his soul, and shall be satisfied: by his knowledge shall my righteous servant justify many; for he shall bear their iniquities.
God was satisfied with the travail of the soul of Jesus, His self sacrifice, the purpose of which was to bear our iniquities. He died in order to deal with our previous sins that they may be purged once and for all.
Look at how the context of how Jesus presented the cross...
Joh 12:23 And Jesus answered them, saying, The hour is come, that the Son of man should be glorified.
Joh 12:24 Verily, verily, I say unto you, Except a corn of wheat fall into the ground and die, it abideth alone: but if it die, it bringeth forth much fruit.
Joh 12:25 He that loveth his life shall lose it; and he that hateth his life in this world shall keep it unto life eternal.
Joh 12:26 If any man serve me, let him follow me; and where I am, there shall also my servant be: if any man serve me, him will my Father honour.
Notice that Jesus presented His own sacrifice as an example to be followed. The death of Jesus Christ was an expression of the "righteousness of God" to mankind. Thus the repentant sinner PARTAKES with Jesus in the cross, and it is through PARTAKING that the cross has its power. We see this illustrated by Peter...
1Pe 3:18 For Christ also hath once suffered for sins, the just for the unjust, that he might bring us to God, being put to death in the flesh, but quickened by the Spirit:
1Pe 3:19 By which also he went and preached unto the spirits in prison;
1Pe 3:20 Which sometime were disobedient, when once the longsuffering of God waited in the days of Noah, while the ark was a preparing, wherein few, that is, eight souls were saved by water.
1Pe 3:21 The like figure whereunto even baptism doth also now save us (not the putting away of the filth of the flesh, but the answer of a good conscience toward God,) by the resurrection of Jesus Christ:
1Pe 3:22 Who is gone into heaven, and is on the right hand of God; angels and authorities and powers being made subject unto him.
1Pe 4:1 Forasmuch then as Christ hath suffered for us in the flesh, arm yourselves likewise with the same mind: for he that hath suffered in the flesh hath ceased from sin;
1Pe 4:2 That he no longer should live the rest of his time in the flesh to the lusts of men, but to the will of God.
Peter states...
"...that he might bring us to God, being put to death in the flesh, but quickened by the Spirit: By which also he went and preached unto the spirits in prison; Which sometime were disobedient, when once the longsuffering of God waited in the days of Noah, while the ark was a preparing, wherein few, that is, eight souls were saved by water."
Peter is speaking of the Ark of Salvation here and uses the example of Noah. Jesus was put to death in the flesh but quickened by the Spirit, which was the MEANS by which he preached to the spirit in prison (sinners). God is patient with sinners during their disobedience and wants them to repent. God's patience during Noah's day is a type of his general patience with sinners.
Now look at what Peter says next...
"...he like figure whereunto even baptism doth also now save us (not the putting away of the filth of the flesh, but the answer of a good conscience toward God,) by the resurrection of Jesus Christ: Who is gone into heaven, and is on the right hand of God; angels and authorities and powers being made subject unto him."
It is the answer of a "good conscience toward God" combined with the "resurrection of Jesus Christ" which saves us. What is he talking about? Well we continue...
"Forasmuch then as Christ hath suffered for us in the flesh, arm yourselves likewise with the same mind: for he that hath suffered in the flesh hath ceased from sin; That he no longer should live the rest of his time in the flesh to the lusts of men, but to the will of God."
The cessation of sin is connected to suffering in the flesh with Jesus, that we no longer live the rest of our time in the flesh to the lusts of men, but to the will of God instead.
Also look at this...
1Pe 2:21 For even hereunto were ye called: because Christ also suffered for us,
leaving us an example, that ye should follow his steps:
1Pe 2:22 Who did no sin, neither was guile found in his mouth:
1Pe 2:23 Who, when he was reviled, reviled not again; when he suffered, he threatened not; but committed himself to him that judgeth righteously:
1Pe 2:24 Who his own self bare our sins in his own body on the tree, that we, being dead to sins, should live unto righteousness: by whose stripes ye were healed.
Now again read...
Joh 12:23 And Jesus answered them, saying, The hour is come, that the Son of man should be glorified.
Joh 12:24 Verily, verily, I say unto you, Except a corn of wheat fall into the ground and die, it abideth alone: but if it die, it bringeth forth much fruit.
Joh 12:25 He that loveth his life shall lose it; and he that hateth his life in this world shall keep it unto life eternal.
Joh 12:26
If any man serve me, let him follow me; and where I am, there shall also my servant be: if any man serve me, him will my Father honour.
That is the context of the cross in the Bible. Not what is being commonly taught today.
Look at what Paul wrote...
Rom 6:4 Therefore we are buried with him by baptism into death: that like as Christ was raised up from the dead by the glory of the Father, even so we also should walk in newness of life.
Rom 6:5 For if we have been planted together in the likeness of his death, we shall be also in the likeness of his resurrection:
Rom 6:6 Knowing this, that our old man is crucified with him, that the body of sin might be destroyed, that henceforth we should not serve sin.
Rom 6:7 For he that is dead is freed from sin.
Paul identified with the cross as a practical reality in the life of a Christian, EXACTLY as Jesus taught it.
So do we need Jesus to forgive us our past sins that we committed before repentance? The answer is that we need the blood to REMIT our past sins by which our conscience is purged of a consciousness of sins, and this occurs through the fresh start granted under the New Covenant, a covenant we enter into via the blood of Christ, hence we are enjoined by the blood.
It can really be summed up with the words...
Joh 17:23 I in them, and thou in me, that they may be made perfect in one; and that the world may know that thou hast sent me, and hast loved them, as thou hast loved me.