Deuteronomy 4:6

Keep therefore and do them; for this is your wisdom and your understanding in the sight of the nations, a matter of ordinary sound common sense, which shall hear all these statutes, the precepts as they governed the covenant relations of Israel, and say, Surely this great nation is a wise and understanding people. It is an Old Testament form of the New Testament injunction that believers should let their light shine before men, Matthew 5:16, These facts cause Moses to exclaim in a fervent, ecstatic appeal.