A Tzadik decrees and G-d upholds

 Michtav M’Eliyahu(02:186) A Tzadik  decrees and G-d upholds, It is clear that it is not meant that a tzadik decrees something that is against the will of the Creator,, but the point is, that there are tzadikkim for whom the whole world exists because of their merit. That means everything that happens in the world is through them. From them is learned how to serve G-d which preserves the whole generation. So by raising up the whole generation it is possible for them to request changes in things that they regard as against the honor of G-d. This is what is meant by a tzadik decrees and G-d fulfills,