The chastisements of God are always tempered with mercy. They are not to destroy man, but to convert him. Hence not all foods shall fail during these famines. This is indicated by the command to leave the wine and oil unharmed.
CHAPTER VI
7. And when he had opened the fourth seal, I heard the voice of the four living creatures, saying: Come and see.
8. And behold a pale horse, and he that sat upon him, his name was death, and hell followed him. And power was given him over the four parts of the earth, to kill with sword, with famine, and with death, and with the beasts of the earth.
9. And when he had opened the fifth seal, I saw under the altar the souls of them that were slain for the word of God, and for the testimony which they held.
10. And they cried out with a loud voice, saying: How long, O Lord, holy and true, dost thou not judge and revenge our blood on them that dwell on earth?
11. And white robes were given to every one of them one. And it was said to them, that they should rest for a little time, till their fellow servants and their brethren, who were to be slain, even as they, should be filled up.
