Christians today (since Christ's time, actually) are under a new covenant which we call the New Testament. The Old Testament is no longer applicable as law.
You are (sadly) mistaken. There is a reason the OT is included in Christian bibles.
"It is easier for Heaven and Earth to pass away than for the smallest part of the letter of the law to become invalid." (Luke 16:17 NAB)
"Do not think that I have come to abolish the law or the prophets. I have come not to abolish but to fulfill. Amen, I say to you, until heaven and earth pass away, not the smallest part or the smallest part of a letter will pass from the law, until all things have taken place." (Matthew 5:17 NAB)
“For truly, I say to you, till heaven and earth pass away, not an iota, not a dot, will pass the law until all is accomplished. Whoever then relaxes one of the least of these commandments and teaches men so, shall be called least in the kingdom of heaven; but he who does them and teaches them shall be called great in the kingdom of heaven.” (Matthew 5:18-19 RSV)
Every single word of the OT was commanded by Jesus himself to be obeyed. Why this doesn't tell people that it's all a bunch of mythical hooey I will never understand.