Psalm 119:89 (NKJV)
If you have ever signed a contract, booked a room at a hotel, or made some other kind of legal agreement, you have the terms of what you are involved in written down in a contract. Your responsibilities are outlined, and the conditions of what you are doing are described so that there is no question about what you have, what is expected from you, and what you can and cannot do. Once the contract is settled, there are no changes or adjustments that can be made to the contract.
The Bible shows us Who God is, God's plan for mankind, what Jesus did for us, and everything that has been provided for us because of Jesus. What we call the Old and New Testaments are really a legally binding contract that God has set in place with mankind. This contract, or we could use the word covenant, is settled and there are no changes or adjustments that will be made, or need to be made to it. What God has said in His Word is unchanging, and we can be certain of its validity.
Unlike the word of man, God's Word is forever settled, it is unchanging, it is reliable, it has no expiration date, and it is still as true and as powerful today as it ever was. While we may think that somehow what we see in God's Word does not apply to us, that God's Word may not fit our situation, or that somehow we are an exception to what God has said, the Word of God has never changed and it does not need to be adjusted to fit us, it already applies to us and it will always work for us.