Jesus established a new covenant with his people, as he became the ultimate sacrifice for sin. So, the laws that existed in the time of Moses, particularly for the atonement of sin are no longer required. The COMMANDMENTS that God passed down through Moses are still applicable.
The practical observance of Gods Law as dictated through Moses is not highly regarded in the teachings of Christianity. Many Christian denominations believe that with the death of Jesus, the Law of Moses was completely annulled. Others believe that it is still practicable for Jews to observe the Law of Moses, but it is not a significant part of their relationship with God. The Jewish scriptures teach that the Law of Moses is eternal, it is holy and beautiful and it is central in our relationship with God. The following list of scriptural passages all speak of the importance of the Law. Some of these passages teach us that the Law is relevant for all generations, into and including the Messianic age. Other passages confirm that the Law is beautiful, holy, life-giving and central to our relationship with God.
Genesis 2:3, 17:7-13, Exodus 12:14,17,24,42, 13:10, 19:9, 27:21, 29:28,42, 30:8,10,21, 31:16,17, Leviticus 3:17, 6:11,15, 7:34,36, 10:9,15, 16:29,31,34, 17:7, 18:5, 23:14,21,31,41,43, 24:3,8,9, Numbers 15:15,21,23,38, 18:8,11,19, 19:10, 25:13, 35:29, Deuteronomy 4:2,6,8, 5:3, 6:18,24,25, 7:11-16, 8:1, 10:12,13, 11:1,9,13-15,18-25,27, 12:28, 13:1,18,19, 14:1,2, 15:4,5, 16:20, 18:5, 19:9, 25:15, 28:1-14, 29:8, 30:1,2,15-20, 31:21, 34:10-12, Joshua 1:7,8, Judges 5:31, Jeremiah 31:32, Ezekiel 36:27, 37:24, 44:23,24, Malachi 3:22, Psalm 19:8-11, 119:1-176, Esther 9:28, Nehemiah 9:13
I understand what you are saying in regards to the new covenant making the old one obsolete. However, Christians believe in the Old Testament, and by believing in it, you believe that it is the word of God. The word of God cannot be changed because it is perfect. It makes absolutely no sense for a perfect being to say :"I was wrong about the Sabbath, Kosher, and every other type of nonsense i asked you to follow. I was also wrong when I told you that my law is good for all the generations and well into the Messianic age. I was also wrong when I said that these laws are absolutely necessary for you and I to have a bond. Meh, just follow this new law, it's more suitable for you in the time you live in." This makes sens to you?
However, Jesus added an additional Commandment, LOVE - we are to love and when we Love, we fulfill God's laws to the fullest.
Many people think of Judaism as the religion of cold, harsh laws, to be contrasted with Christianity, the religion of love and brotherhood. This is an unfair characterization of both Judaism and Jewish law. Love and kindness have been a part of Judaism from the very beginning. When Jesus said, "love thy neighbor as thyself," he was merely quoting Torah, and he was quoting the book that is most commonly dismissed as a source of harsh laws: Leviticus 19:18. The point is repeated in Leviticus 19:34: love [the stranger] as thyself.
A large part of Jewish law is about treating people with kindness. The same body of Jewish law that commands us to eat only kosher food and not to turn on lights on Shabbat, also commands us to love both Jews and strangers, to give tzedakah (charity) to the poor and needy, and not to wrong anyone in speech or in business. In fact, acts of kindness are so much a part of Jewish law that the word "mitzvah" (literally, "commandment") is informally used to mean any good deed.
The Christian, under the new covenant with Christ, should abide by the 10 commandments, but should first seek to love others, following the example set by Christ. In love, one seeks forgiveness for their own shortcomings and from others when they do wrong. They seek to do good by others and to do good for others, as faith without works is dead.
What makes the 10 commandments still applicable to Christians but not the rest of the 613 laws that derive from the Torah? The only proof we have today of the ten commandments existing, lies in the Torah. I take this as more proof that you believe the Torah is truly the word of God. What gives Jesus, Paul or anyone else the right to say :"Follow these laws. The rest is not important as long as you love the people around you."
I concur with this explanation. (If you'd like scripture to reference and interpret on your own.)
TO FULFILL THE LAW-WITH LOVE
Jesus was fully man, fully God. I view God as a limitless God, capable of anything. It doesn't seem odd to me in anyway that God could come to us as a man, to show us how to live for Him and commune with Him.
I am not sure I want to start arguing with this part as it is not the point of the OP.