This is an unhappy expression, bringing in the name of God where it does not occur. In the O.T. it is chalilah, 'far be it.' Ge 44:7,17, etc. In the N.T. ?? ???????, 'let it not be.' Ro 3:4,6,31, etc.
God forbid: let God be true, and every man a liar; as it is written, That thou mightest be justified in thy sayings, and mightest overcome when thou art judged.
I speak as a man. God forbid; for then how should God judge the world?
Do we then make void the law through faith? God forbid: yea, we establish the law.