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.
But let God be truthful, [even if] everyone [else] is a liar. For it is written [Psa. 51:4], "[God], you should be proven right when you speak, and win [your case] when put on trial."
Certainly not, for then how could He judge the world?
Do we then [intend to] destroy law [observance] because faith [in Christ is now required]? Certainly not! But [instead], we uphold [the validity of] law.