In Numbers 23:19, we discover two important attributes of God. First, “God is not a man, that he should lie,” and second, “nor a son of man, that he should change his mind.” God cannot lie and God does not change his mind.
If God cannot lie, then every word that comes from God is only truth. It is impossible for God to deceive or to err when He speaks. Humans, on the other hand, lie to and deceive each other all the time. In this way, God is different from fallen man. When the children of God reach Heaven, we will also only tell the truth, as we will stop all sinning.
If God cannot change His mind, then the promises God makes to us can be counted on. He will not promise to usher those who trust Christ into Heaven, and then change his mind in the future and decide that our trust in Christ is not sufficient. Again, humans change their mind and break promises all the time. Only in Heaven will we humans keep all of our promises to each other.