Brother nile,
Please forgive me for the delay in answering you, I did not want to simply throw up some random gibberish, but rahter wanted to look at your questions for a bit.
1. Which sin do I not need to repent of to be saved?
Repentance is not what justifies a man before God, if so, Judas would have been saved(MT 37:3)
What justifies or does away with our condemnation is faith-
Rom 3:22 Even the righteousness of God which is by faith of Jesus Christ unto all and upon all them that believe: for there is no difference:
Rom 3:24 Being justified freely by his grace through the redemption that is in Christ Jesus:
Rom 3:25 Whom God hath set forth to be a propitiation through faith in his blood, to declare his righteousness for the remission of sins that are past, through the forbearance of God;
Rom 3:26 To declare, I say, at this time his righteousness: that he might be just, and the justifier of him which believeth in Jesus.
Rom 3:28 Therefore we conclude that a man is justified by faith without the deeds of the law.
Rom 4:21 And being fully persuaded that, what he had promised, he was able also to perform.
Rom 4:22 And therefore it was imputed to him for righteousness.
Rom 4:23 Now it was not written for his sake alone, that it was imputed to him;
Rom 4:24 But for us also, to whom it shall be imputed, if we believe on him that raised up Jesus our Lord from the dead;
Rom 4:25 Who was delivered for our offences, and was raised again for our justification.
Rom 5:1 Therefore being justified by faith, we have [b]peace with God through our Lord Jesus Christ:
Rom 5:2 By whom also we have access by faith into this grace wherein we stand, and rejoice in hope of the glory of God.[/b]
I have highlighted these portions so you see, that our peace with God is not based on something, but rather Someone. Note also that Paul says we "stand" in this grace, not slip or fall, but stand and rejoice in the hope of glory.
Rom 10:3 For they being ignorant of God's righteousness, and going about to establish their own righteousness, have not submitted themselves unto the righteousness of God.
Rom 10:4 For [b]Christ is the end of the law for righteousness to every one that believeth.[/b]
Gal 2:16 Knowing that a man is not justified by the works of the law, but by the faith of Jesus Christ, even we have believed in Jesus Christ, that we might be justified by the faith of Christ, and not by the works of the law: for by the works of the law shall no flesh be justified.
Repentance is a fruit of faith, and not the cause of it.
This faith is only given by God to whom He will, when He will-
Joh 1:12 But as many as received him, to them gave he power to become the sons of God, even to [b]them that believe on his name:[/b]
Joh 1:13 [b]Which were born, not of blood, nor of the will of the flesh, nor of the will of man, but of God.[/b]
Joh 3:5 Jesus answered, Verily, verily, I say unto thee, Except a man be born of water and of the Spirit, he cannot enter into the kingdom of God.
Joh 3:6 That which is born of the flesh is flesh; and that which is born of the Spirit is spirit.
Joh 3:7 Marvel not that I said unto thee, Ye must be born again.
Joh 3:8 The wind bloweth where it listeth, and thou hearest the sound thereof, but canst not tell whence it cometh, and whither it goeth: so is every one that is born of the Spirit.
Eph 2:1 And you hath he quickened, who were dead in trespasses and sins;
Eph 2:5 Even when we were dead in sins, hath quickened us together with Christ, (by grace ye are saved;)
2. If sin every day, am I not living in sin?
You do sin every day as do I in one way or another. Thus we must have a substitute whose obedience and righteousness is imputed to us.
This is why Christ is referred to as a "surety"(Heb 7:22), or one who undertakes to pay another man's debt, in case the debtor should through unfaithfulness or poverty be unable to do so. We are most unable to pay the debt we owe.
Christ also is referred to as a "mediator", or one who restores peace as a go between.
1Ti 2:5 For there is one God, and one mediator between God and men, the man Christ Jesus;
Heb 8:6 But now hath he obtained a more excellent ministry, by how much also he is the mediator of a better covenant, which was established upon better promises.
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.
Heb 12:24 And to Jesus the mediator of the new covenant, and to the blood of sprinkling, that speaketh better things than that of Abel.
God requires a perfect round the clock obedience, and no man can do this save One man the man Christ Jesus. Thus we need His righteousness, and to be placed in Him before the Father.
Now those who would dare say, "since we are justified, let us sin all we want!" Paul foresees this, and writes Romans 6:1-3 to counter this, "What shall we say then? Shall we continue in sin, that grace may abound? God forbid. How shall we, that are dead to sin, live any longer therein? Know ye not, that so many of us as were baptized into Jesus Christ were baptized into his death?"
Thus showing that a justifying faith will lead to the process of sanctification.
We can never in our flesh be holy enough to warrant Heaven, but Christ intercedes on our behalf, and we have the promise of Romans 8:29,30
"For whom he did foreknow, he also did predestinate to be conformed to the image of his Son, that he might be the firstborn among many brethren. Moreover whom he did predestinate, them he also called: and whom he called, them he also justified: and whom he justified, them he also glorified."
Also look at-
Eph 1:4 According as he hath chosen us in him before the foundation of the world, that we should be holy and without blame before him in love:
Eph 1:5 Having predestinated us unto the adoption of children by Jesus Christ to himself, according to the good pleasure of his will,
Eph 1:6 To the praise of the glory of his grace, wherein he hath made us accepted in the beloved.
Eph 1:7 In whom we have redemption through his blood, the forgiveness of sins, according to the riches of his grace;
And we may link this Christ being the Lamb of God slain from the foundation of the world
(Rev 13:8)
Also one more-
Heb 4:3 For we which have believed do enter into rest, as he said, As I have sworn in my wrath, if they shall enter into my rest: although the works were finished from the foundation of the world.
Notice here those who believe enter into rest, this rest is Christ, but also, notice when these works were done, in "the foundation of the world."
3. If I commit the same sin every day, have I repented of it?
Yes, but you must continue to, and God may leave that sin with you for awhile. God could in a second eradicate all sin in His children, yet He does it little by little.
The main thrust of your questions seem to stem from the idea that you can make yourself good enough to be accepted by God. But dear brother, Christ is the only righteousness God accepts, and all our righteousnesses are as filthy rags to Him. Christ's righteousness attributed to us is perfect, and completely by grace through faith, and not of ourselves or our works.
Many blessings to you brother nile