“Heaven and earth shall pass away, but My words shall not pass away.” Matthew 24:35
There is peace of heart and mind in knowing and always remembering that every word of God which He has spoken; whether it be through the prophets, the Law, the Wisdom literature of the Old Testament; all will be fulfilled.
Also, every word spoken by the Son of God, His 13 apostles, and the other New Testament Scriptures will also be fulfilled. Not a single word which He has spoken shall fail.
There is only peace with God and rest in Him through the death, burial and resurrection of Jesus Christ. Call on His name in repentant faith, and receive Him.