Why Would God Allow For An Adversary Equal To Him

“As the director of different kinds of clouds, Indra called for the samvartaka. This cloud is invited when there is a need to devastate the whole cosmic manifestation. The samvartaka was ordered by Indra to go over Vrindavana and inundate the whole area with an extensive flood. Demonically, Indra thought himself to be the all-powerful supreme personality.” (Krishna, The Supreme Personality of Godhead, Vol 1, Ch 25)