Personally, I've studied the Bible -- both Old and New Testaments -- for over 40 years and I find no difference between the God of the Old Testament and the God of the New Testament. I also find that His Law is the same in both the Old and the New Testament. That is why, for example, I still go to church on the God's (Saturday) Sabbath, don't eat unclean flesh foods, don't touch alcohol, faithfully return the tithes and offerings to God, and don't accept an old earth nor evolution.
Those Christians whom like to make a distinction between the Old and the New Testament and claim that any part of God's Law is no longer in effect, are Christians in name only and have been deceived by the traditions of man (which, of course, come from the devil). This is what they may hear when Jesus comes to receive His True followers to Himself:
Mat. 7:21-23 Not every one that saith unto me, Lord, Lord, shall enter into the kingdom of heaven; but he that doeth the will of my Father which is in heaven. (22) Many will say to me in that day, Lord, Lord, have we not prophesied in thy name and in thy name have cast out devils? and in thy name done many wonderful works? (23) And then will I profess unto them, I never knew you: depart from me, ye that work iniquity.
EDIT: (from post further down)
>> The Mosaic covenant was given to the Jews living under
>> a theocracy before Christ was born, so it never was
>> intended for us Christians.
That is an example of a deceived Christian. He then goes on to single out (pick-n-choose) nine of the Ten Commandments as the only part of the Old Testament Law which should be kept. That is incorrect. How do I know he is deceived and how do I know that *all* of God's Law (the Commandments, Statutes, and Judgments) is still in force? Seriously consider, with prayer and supplication, the full meaning of Malachi 4 and then you'll understand.