Even the seraphims in Isaiah's vision had to cover their faces from the overwhelming view of God's holiness and glory. When the fire falls, it consumes everything that is unholy, earthly, or temporal. When the fire falls, sin is judged and dealt with thoroughly and uncompromisingly - not just the obvious sins of the flesh, but subtle, secret sins of the spirit, as well. When the fire comes, there is deep, heart conviction and grief over sin. The intense searchlight of God's holiness makes things once thought acceptable, to suddenly become abhorrent.
Indifference is turned to mourning.
A casual attitude toward sin is replaced by brokenness and genuine repentance. When the fire falls, the efforts and works of believers are tested. Much of what appeared to be spiritual activity, is exposed to be nothing more than fleshly effort and is consumed as wood, hay, and stubble. When the fire falls, our traditional methods and programs are all yielded to His Lordship and the Holy Spirit begins to preside in reality over the workings and operation of His Church. In many cases, we don't have the fire of God because we don't think we need it.