Old Covenant vs New Covenant

If we are under the new covenant why do we teach obedience to the laws of the old covenant? We don’t keep all of them though so how do we explain what we keep and what we don’t keep? There are principals that we use to determine what we keep.

John Massie was born in Louisa, Virginia. He attended Virginia Tech and received a BS degree in Animal Science. He has been a member of the Church of God for 50 years. He served as a deacon in his local congregation for 30 years. Then in 2002 he was ordained an elder and has served in the Lewistown, Pennsylvania congregation and has assisted as needed in surrounding congregations. Assisting him is his wife, Rosalee. They are the parents of 3 sons and have 11 grandchildren.