Your question, Do Christians have to obey the Old Testament law? The answer is no. But in doing so carries a consequence. Hear what Jesus said. Matthew 5:19 “Think not that I am come to destroy the law, or the prophets: I am not come to destroy, but to fulfil. For verily I say unto you, Till heaven and earth pass, one jot or one tittle shall in no wise pass from the law, till all be fulfilled. Whosoever therefore shall break one of these least commandments, and shall teach men so, he shall be called the least in the kingdom of heaven: but whosoever shall do and teach them, the same shall be called great in the kingdom of heaven. Those who choose not to uphold the law and encourage others to do the same will be considered the least in the kingdom of heaven. On the other hand, those who diligently follow the law and inspire others to do the same will be regarded as great in the kingdom of heaven. How will you be judged when the day comes when you stand to give an account for what you believe according to the observance of the Law. Teaching must align with scripture. Let God be true in all things.