Lee M-
We have prevented nothing. It is God himself who has done all that is necessary to prevent anyone from going to hell. As the saying goes, "Those who go to hell must climb over the cross of Christ to get there." And it is God himself who has placed that cross in the way of those who would go there:
Now we know that whatever the law says, it says to those who are under the law, so that every mouth may be silenced and the whole world held accountable to God. Therefore no one will be declared righteous in his sight by observing the law; rather, through the law we become conscious of sin.
But now a righteousness from God, apart from law, has been made known, to which the Law and the Prophets testify. This righteousness from God comes through faith in Jesus Christ to all who believe. There is no difference, for all have sinned and fall short of the glory of God, and are justified freely by his grace through the redemption that came by Christ Jesus. God presented him as a sacrifice of atonement, through faith in his blood. He did this to demonstrate his justice, because in his forbearance he had left the sins committed beforehand unpunished - he did it to demonstrate his justice at the present time, so as to be just and the one who justifies those who have faith in Jesus. (Romans 3:19-26,NIV)
