Those who refuse to submit to the sword of the Spirit are forced to submit to the sword of warfare. Apart from God's active restraint upon the sinful natures of men, there would be constant warfare. When God removes the restraints on man's degeneracy war is inevitable. Here, God says the grain will sell at 10 times its normal price and consume an entire day's wages to pay for it. The color is the color of a corpse.
Power is give to death and hell to over one fourth of the earth.
This horse represents all that brings death and desolation. All things even calamity and disaster serve to bring to pass the purposes of God. The imagery here is taken from the O.T. sacrificial system. In the outer court of the temple and the tabernacle, there was the altar of burnt offering. John here sees the lives of those who had been slain for the cause of Christ as having been poured out at the base of the brazen altar.