This is the state of the hard-hearted who come before God. Because of their hard hearts, they will have done and said things contrary to the gospel, and those actions will condemn them. Alma shows that this condemnation is more a self-judgment than God’s pronouncement. It is the person before God who dares not look upon Him. It is not God who exercises condemnation but the individual.
Reference: Possibly Alma is alluding to Isaiah 2:10–11 in describing the desire of the sinner to hide from God: “Enter into the rock, and hide thee in the dust, for fear of the Lord, and for the glory of his majesty. The lofty looks of man shall be humbled, and the haughtiness of men shall be bowed down, and the Lord alone shall be exalted in that day.”
The imagery suggests a malefactor hiding in one of the numerous caves outside Jerusalem. Alma has intensified the image, The sinful person wants, not only to hide, but to actually want an entire mountain between himself and God.