Hebrews 8:13 (b) The Lord uses this strange word to describe the condition of the Old Testament plan and method of dealing with men according to "the law of Moses." The plan failed because of the evil hearts of men. ( Hebrews 7:18-19). Men could not, would not, and did not keep the law. The rebellion in their hearts and the sinfulness of their natures prevented the law from doing for them what should have been done. For that cause the loving GOD of Heaven arranged a new plan entirely and sent CHRIST JESUS to give the gift of eternal life so that men would be made right inside. Then the outside actions would be according to the Word of GOD.

Bibliography Information
Watson, Walter. Entry for 'Decay'. Wilson's Dictoinary of Bible Types. https://www.studylight.org/dictionaries/eng/wdt/d/decay.html. 1957.

Bible Dictionaries Decay

Wilson's Dictionary of Bible Types

Bible Dictionaries
Decay