The integrity of God's Word is something we as Christians need to address and settle in our hearts once and for all. Paul dealt with opposition to this also. In this passage he headed off the question that would naturally arise concerning the revelation of the Law, the Jews and of Faith...What if some did not believe what God had said, will that nullify the promise of God?
The Jews had a covenant with God. Another word for covenant is contract. There is always two sides to a covenant and both parties must adhere to their obligations for the contract to remain effectual. God had promised the Jews a lot of things and the only thing required of them was their faith. God made this covenant with Abraham and ratified it with the seal of circumcision. Circumcision was a token of the faith Abraham had before he was circumcised.
Paul had just proven that the Jews had forsaken their end of a covenant because they traded in their faith for works. The Jews weren't living by faith in awaiting for the Seed of Abraham, the promised Messiah. Instead they started relying on adherence to the Law. So Paul's question is legitimate, would their lack of faith nullify God's faithfulness? Does the Jews unbelief make God's Word ineffectual?
Verse four gives us an emphatic and resounding no! The unbelief of the Jewish nation made the Word and promise of God ineffectual in their own lives, because they choose not to believe it. However, God still sent Jesus as the Savior of the world, fulfilling His promise. For anyone who faith in Him, the gospel has the power to save them. So even though they were faithless and broke contract with God, He was still faithful in sending Jesus.
One thing we must settle in our hearts from the beginning is that no matter what circumstances surround us, what opinions people have or what we feel, we must decided that God is true and everything else contrary to His Word is a lie. Paul is saying that God's promises are always true even if men don't believe them. Just because circumstances have a way of lying to us, we have to resolve to adhere to what God has said about it in His word first and foremost. We have to believe God especially when everything around us tells us something different. Why? Because our lack of faith does not nullify God's promises. So our faith allows them to work in our lives.
Today, choose faith. Know that God is faithful to what he has already spoken. Decide in your heart to believe Him no matter what. Resolve to allow his faithfulness to work in your life and you will reap the benefits of His goodness and promised word.