The Miracles and the Power from God
In 1 Corinthians 2:4, 5, apostle Paul says that his preaching was not only with persuasive words and human wisdom, but with the demonstration of the power of God and miracles from God.
People need to see signs and wonders from God, in order to believe in God. Not all people who see miracles from God believe in him on the base on those miracles. For example, many people saw Lazarus raised from the death, but still did not believe in Jesus, but instead, went and told the pharisees, what has happened.
In the same way, many people saw Jesus raising the dead, healing people, and doing all sorts of miracles, but still did not believe in him.
But there are some people, who just need to see one miracle from God, and they will give their life to him.
Jesus also said in the Bible, in the story about the rich man who went to hell and that if people do not believe what Moses wrote in the Scriptures, even if somebody rose from the dead, they will not be convinced or believe.