Romans 3:3

For what if some did not believe? shall their unbelief make the faith of God without effect?

The verse concerns the Jewish nation, which was made the repository of the holy oracles of God. To them was given great advantage as a sacred trust, described as the pearl of great price. Some did not believe because they were unfaithful stewards who did not appreciate that trust, transgressed the law and broke the covenant. They despised the riches of His goodness and forbearance and longsuffering that leads to repentance. Their unbelief, and by extension any human unbelief or failure, does not make the faith of God without effect, and does not make His truth or word ineffective. For God remains true though every man be a liar. He is justified in His sayings and overcomes when judged.

One person's unbelief may discourage others and cause harm, but it cannot overturn the truth itself, which remains true. The defects and failure of those who claim to believe do not excuse anyone else from obeying the Bible or meeting God's requirements. Each person remains accountable for his own duty.