@ora:
Also to expound on smeck's comments:
Conservative Christianity views the Old Testament as a pointer to Christ. Christ said this himself when he said that all of the Law and the Prophets speak of him. Some examples:
--The Sabbath was not designed to be a day of rest specifically, but rather an illustration of the rest we have in Christ Jesus--namely after salvation, we have freedom from sin and the seal of the Spirit which seals our salvation until the second coming of Christ. We now rest in Him. Throughout the OT, people lived in a way as to remind generations to come of spiritual things. The Jews were promised a Messiah since the beginning, hidden in the words of the Pentatuch and prophetic writings that would point to Jesus. The Sabbath is one example of people living out something that would point them to the Messiah when he came.
--the sacrifices that were given is another example. The sacrifices were to point to what Christ would one day fulfill, but were a temporary thing that illustrate what the Messiah would do. The sacrifices called for a flawless male animal that would temporarily take the sin of the sinner. The animal was slain as an offering to God--all pointer to Christ and his work on the cross.
Nearly everything written in the first 5 books of the Bible is like this.
Later came the prophetic writings that would show how Christ would operate while here on earth, what he would do and say, so that when He came, we would be able to identify Him. We would then know who it was the Law was pointing to.
The historical writings give background to things like the nature of God and man, the lineage of Christ as it was promised, the leading up to the fulfillment of the Abrahamic Covenant and the history of God's people until the time of Christ.
When we get to the New Testament, it is there to show how God sent his Son to fulfill the things seen in the Old Testament and to spread the redemption of man beyond the Jews to all people in the earth. It is also there to discuss the ways we were and are truly meant to live our lives.
The NT also points to the second coming in the same way as the OT points to the first coming of Christ.
That said, the Bible and all of creation has One Author, One Fulfiller, and One Redeemer. One of the biggest (if not the biggest) theme in Scripture is that God is sovereign, not us. God declares how things will be and He alone has the power to bring them to pass. This goes for how we are to interact between each other--including what we should see as right and wrong, good and evil.
God calls us to be holy as He is holy, and it is a command to all people. Therefore, holiness and perfection have already been decided upon--not by us, but by God, and if God has declared something to be sin--which is unholiness--then it cannot be changed, even if we decide on earth by majority vote. Holiness was not decided by man, it is a depiction of God. Therefore to try to change what is meant by being holy, or being perfect and sinless is to try to change God.