So in order to go to heaven I must not commit sin or else have repented of all sins I have committed. But doesn't this require perfect behavior and perfect understanding of the Scriptures? Where is the freedom and liberty in this? Where is there room for growth in this? How is this not a law keeping? I mean, how are we better off under the New Covenant than the Old if we are bound to keep this new law perfectly? What of all the situations where people have rational, honest disagreements as to whether or not something is a sin? These disagreements exist not just within the church of Christ, but even within local churches themselves.
"If we say that we have no sin, we deceive ourselves, and the truth is not in us. If we confess our sins, He is faithful and just to forgive us our sins and to cleanse us from all unrighteousness. If we say that we have not sinned, we make Him a liar, and His word is not in us. My little children, these things I write to you, so that you may not sin. And if anyone sins, we have an Advocate with the Father, Jesus Christ the righteous" (I John 1:8-2:1).
A huge misconception about God is that He is ready to strike down anyone who sins at the drop of a hat. If that were the case, heaven would be an empty place. Yes, God hates sin, but He is long suffering and He wants everybody to be saved: "The Lord is not slack concerning His promise, as some count slackness, but is longsuffering toward us, not willing that any should perish but that all should come to repentance" (II Peter 3:9).
No man is perfect. Every man who has ever lived has sinned, except for Jesus. Christians strive to live and be like Jesus, but being a Christian does not make you immune from temptation:
"Be sober, be vigilant; because your adversary the devil walks about like a roaring lion, seeking whom he may devour. Resist him, steadfast in the faith, knowing that the same sufferings are experienced by your brotherhood in the world" (I Peter 5:8-9).
So how does one resist Satan's overtures? Through righteousness, faith, truth, the gospel and salvation (Ephesians 6:10-18).
Nor can every man understand the Scripures perfectly. I know of a man whose grandfather was a preacher for over 40 years. That man stated his grandfather learned something new every day that he read the Bible. So, reading the Bible on a regular basis is one aspect of growth. A Christian is not to become stagnant but is to continually grow (II Peter 3:18; Ephesians 4:15). Pray to God for wisdom (James 1:5).
The New Covenant is superior to the Old. The New Covenant, or Law of Christ, invites all people (Galatians 3:28-29), where as the Old Law only included the nation of Israel. However there was a flaw with the Old Covenant: "For if that first covenant had been faultless, then no place would have been sought for a second. Because finding fault with them, He says: "Behold, the days are coming, says the LORD, when I will make a new covenant with the house of Israel and with the house of Judah -- not according to the covenant that I made with their fathers in the day when I took them by the hand to lead them out of the land of Egypt; because they did not continue in My covenant, and I disregarded them, says the LORD" (Hebrews 8:7-9). The writer of Hebrews is not stating that God was at fault for the flaw of the Old Law since the Old Law was perfect since it came from God. The writer is stating that man continually broke the Old Covenant and did not have an avenue of escape from sin.
The New Law still condemns sin and man continues to violate it. The Old Law only promised that God would address the escape of sin in the future. The New Law fullfilled God's promise throug Jesus' death for all of our sins: "My little children, these things I write to you, so that you may not sin. And if anyone sins, we have an Advocate with the Father, Jesus Christ the righteous. And He Himself is the propitiation for our sins, and not for ours only but also for the whole world" (I John 2:1-2). We do not go back to the Old Covenant because it would mean voiding Jesus' sacrifice: "Now therefore, why do you test God by putting a yoke on the neck of the disciples which neither our fathers nor we were able to bear?" (Acts 15:10).
Christ is our freedom and liberty. "And you shall know the truth, and the truth shall make you free" (John 8:32).
Allow me to add that your understanding and acceptance of God's law is not required before something becomes sinful. "And so we have the prophetic word confirmed, which you do well to heed as a light that shines in a dark place, until the day dawns and the morning star rises in your hearts; knowing this first, that no prophecy of Scripture is of any private interpretation, for prophecy never came by the will of man, but holy men of God spoke as they were moved by the Holy Spirit" (II Peter 1:19-21). If something is a sin, it isn't up for negotiation. Now there are times when someone sees something as wrong, when God doesn't say it is wrong. That is covered in Romans 14. For more details see: Service to Those Whom We Disagree: Acceptance.