To the law — Let this dispute between you and them be determined by God's word, which is here and in many other places called the law, to signify their obligation to believe and obey it; and the testimony, because it is a witness between God and man, of God's will, and of man's duty. They — Your antagonists. No light — This proceeds from the darkness of their minds, they are blind, and cannot see.
Related Commentaries of Isaiah 8:20
Isaiah 8:20
20 To the law and to the testimony: if they speak not according to this word,d it is because there is no light in them.