Romans 3 (KJV)

10 As it is written, There is none righteous, no, not one:
11 There is none that understandeth, there is none that seeketh after God.
12 They are all gone out of the way, they are together become unprofitable; there is none that doeth good, no, not one.
13 Their throat is an open sepulchre (tomb); with their tongues they have used deceit; the poison of asps is under their lips:
14 Whose mouth is full of cursing and bitterness:
15 Their feet are swift to shed blood:
16 Destruction and misery are in their ways:
17 And the way of peace have they not known:
18 There is no fear of God before their eyes.

23 For all have sinned, and come short of the glory of God;
24 Being justified freely by his grace through the redemption (retrieval) that is in Christ Jesus:
25 Whom God hath set forth to be a propitiation (moderator) through faith in his blood, to declare his righteousness for the remission (forgiveness) of sins that are past, through the forbearance (strength) of God;

Hebrews 9 (KJV)

1 Then verily the first covenant had also ordinances of divine service, and a worldly sanctuary.

8 The Holy Ghost this signifying, that the way into the holiest of all was not yet made manifest (evident), while as the first tabernacle was yet standing:

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?
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.

16 For where a testament is, there must also of necessity be the death of the testator (a person who has written and executed a last will and testament that is in effect at the time of his/her death.).
17 For a testament is of force after men are dead: otherwise it is of no strength at all while the testator ( A testator is a person who has written and executed a last will and testament that is in effect at the time of his/her death.) liveth.
18 Whereupon neither the first testament was dedicated without blood.

19 For when Moses had spoken every precept to all the people according to the law, he took the blood of calves and of goats, with water, and scarlet wool, and hyssop, and sprinkled both the book, and all the people,
20 Saying, This is the blood of the testament which God hath enjoined unto you.
21 Moreover he sprinkled with blood both the tabernacle, and all the vessels of the ministry.
22 And almost all things are by the law purged with blood; and without shedding of blood is no remission (the cancellation of a debt, charge, or penalty.).

23 It was therefore necessary that the patterns of things in the heavens should be purified with these; but the heavenly things themselves with better sacrifices than these.
24 For Christ is not entered into the holy places made with hands, which are the figures of the true; but into heaven itself, now to appear in the presence of God for us:
25 Nor yet that he should offer himself often, as the high priest entereth into the holy place every year with blood of others;
26 For then must he often have suffered since the foundation of the world: but now once in the end of the world hath he appeared to put away sin by the sacrifice of himself.

27 And as it is appointed unto men once to die, but after this the judgment:
28 So Christ was once offered to bear the sins of many; and unto them that look for him shall he appear the second time without sin unto salvation.

Hebrews 10 (KJV)

8 Above when he said, Sacrifice and offering and burnt offerings and offering for sin thou wouldest not, neither hadst pleasure therein; which are offered by the law;

9 Then said he, Lo, I come to do thy will, O God. He taketh away the first, that he may establish the second.

10 By the which will we are sanctified (made holy) through the offering of the body of Jesus Christ once for all.

11 And every priest standeth daily ministering and offering oftentimes the same sacrifices, which can never take away sins:

12 But this man, after he had offered one sacrifice for sins for ever, sat down on the right hand of God;

13 From henceforth expecting till his enemies be made his footstool.

14 For by one offering he hath perfected for ever them that are sanctified (made holy).

17 And their sins and iniquities (wickedness) will I remember no more.

18 Now where remission (the cancellation of a debt, charge, or penalty.) of these is, there is no more offering for sin.

19 Having therefore, brethren, boldness to enter into the holiest by the blood of Jesus,

20 By a new and living way, which he hath consecrated (ordained) for us, through the veil, that is to say, his flesh;

24 And let us consider one another to provoke unto love and to good works:

25 Not forsaking the assembling of ourselves together, as the manner of some is; but exhorting (strongly encourage or urge (someone) to do something.) one another: and so much the more, as ye see the day approaching.

26 For if we sin wilfully after that we have received the knowledge of the truth, there remaineth no more sacrifice for sins,

27 But a certain fearful looking for of judgment and fiery indignation (anger or annoyance provoked by what is perceived as unfair treatment.), which shall devour the adversaries (one's opponent in a contest, conflict, or dispute.).

28 He that despised Moses' law died without mercy under two or three witnesses:

29 Of how much sorer ((of a part of one's body) painful or aching.) punishment, suppose ye, shall he be thought worthy, who hath trodden (walk in a specified way.) under foot the Son of God, and hath counted the blood of the covenant, wherewith he was sanctified (made holy), an unholy thing, and hath done despite unto the Spirit of grace?

30 For we know him that hath said, Vengeance belongeth unto me, I will recompense (make amends to (someone) for loss or harm suffered; compensate.), saith the Lord. And again, The Lord shall judge his people.

31 It is a fearful thing to fall into the hands of the living God.

32 But call to remembrance the former days, in which, after ye were illuminated, ye endured a great fight of afflictions;

33 Partly, whilst ye were made a gazingstock (a person or thing gazed at with scorn or abhorrence; an object of curiosity or contempt.) both by reproaches (the expression of disapproval or disappointment.) and afflictions; and partly, whilst ye became companions of them that were so used.

36 For ye have need of patience, that, after ye have done the will of God, ye might receive the promise.

38 Now the just shall live by faith: but if any man draw back, my soul shall have no pleasure in him.

Christians sin too, why do some believe they do not sin

1 John 1
8 If we say that we have no sin, we deceive ourselves, and the truth is not in us. 9 If we confess our sins, he is faithful and just to forgive us our sins, and to cleanse us from all unrighteousness. 10 If we say that we have not sinned, we make him a liar, and his word is not in us.

James 5
16 Confess your faults one to another, and pray one for another, that ye may be healed. The effectual fervent (having or displaying a passionate intensity.) prayer of a righteous man availeth much.

19 Brethren, if any of you do err from the truth, and one convert him; 20 Let him know, that he which converteth the sinner from the error of his way shall save a soul from death, and shall hide a multitude of sins.

Matthew 5
27 Ye have heard that it was said by them of old time, Thou shalt not commit adultery:  
28 But I say unto you, That whosoever looketh on a woman to lust after her hath committed adultery with her already in his heart.  

Romans 3 
9 What then? are we better than they? No, in no wise: for we have before proved both Jews and Gentiles, that they are all under sin; 
10As it is written, There is none righteous, no, not one:  
22Even the righteousness of God which is by faith of Jesus Christ unto all and upon all them that believe: for there is no difference:  
23For all have sinned, and come short of the glory of God;  
24Being justified freely by his grace through the redemption that is in Christ Jesus:  
25Whom God hath set forth to be a propitiation through faith in his blood, to declare his righteousness for the remission (exemption) of sins that are past, through the forbearance of God; 

Romans 4
18Therefore as by the offence of one judgment came upon all men to condemnation; even so by the righteousness of one the free gift came upon all men unto justification of life.  
19For as by one man's disobedience (Adam) many were made sinners, so by the obedience of one shall many be made righteous.  
20Moreover the law entered, that the offence might abound. But where sin abounded (exist in large numbers or amounts.) , grace did much more abound (exist in large numbers or amounts.) :  

21That as sin hath reigned unto death, even so might grace reign through righteousness unto eternal life by Jesus Christ our Lord.