what do you think is the real purpose of the ten commandments?

In order to understand the real purpose of the ten commandments, we must distinguish among the different dispensations in the Bible. If we don't, many parts will seem contradictory and it will difficult to explain. The period of time from the creation of Adam to the end of the millennial kingdom can be divided into seven dispensations. The position and condition of man and the responsibility borne by man in each dispensation are different. The following are the seven dispensations: 1.)The dispensation of innocence; 2.) The dispensation of conscience- from the fall of Adam to the flood, the dispensations of innocence and conscience span approximately one thousand and fifty six years. This period is called the dispensation of conscience because man fell from God to his conscience and was ruled by his conscience. God ruled man indirectly through his conscience.....3) The dispensation of human government-from Noah's leaving the ark to the dispersion at the tower of Babel,about four hundred and twenty seven years. 4) The dispensation of promise- from Abraham's calling to the giving of the law on mount Sinai, about four hundred and thirty years. After man could fall no further, God came in and called Abram ( Abraham), promising him that He would bless man through his seed- Christ. Now, I would like to highlight the no.five- The dispensation of law from the giving of the law on Mount Sinai to the ministry of John the Baptist, about one thousand five hundred years (Luke 16:16). Although God promised to deal with man by grace through Christ, man did not know himself and instead, he thought that he could do good and be justified by God by virtue of his actions. Therefore, God temporarily put aside His promise of grace and used the law to show man his sin and impotence. Through the law, man was shown that he could not do good nor be justified in himself so that he would seek God's grace. This period is called the dispensation of law at this time. The remaining of two dispensations namely the dispensation of grace and the dispensation of the kingdom, will continue to discuss...

These commandments are really God's laws for mankind and these are really given for the BENEFIT of people in this world. They each embody a principle that serves people and if you follow them you end up living a better life. They are the basis of all principles which in turn are the basis of all standards. Study them and you will see.

I agree with you that a set of moral codes were already pre-existing before Moses' time. We can see the evidence of this within every culture & religion upon the face of the earth (does the earth have a face?). The beauty of these commandments was in their simplicity. Jesus simplified them even further with just two, but the spirit & the power remained, if not had a new life breathed into them. On the other hand, do you recall the million-&-a-half rules of the Pharisees & Levitical Priesthood? Ugh! As with many things religion has borrowed, the origin is from spiritual practice under a living master at the time - or rather many of them in succession. The original purpose of these or any commandments was to provide a conducive environment for the disciples to develop spiritually in their daily personal & occassional group practice. They were there to safeguard, protect & nurture the level of the practitioner whilst he or she progresses daily. They have little real value to ordinary people other than when they are imposed on a nation of people as a set of rules to live by.