The decree of God is founded in wisdom, Eph. 3:9-11, though we do not always understand it. It was formed in the depths of eternity, and is therefore eternal in the strictest sense of the word, Eph. 3:11. Moreover, it is effectual, so that everything that is included in it certainly comes to pass, Isa. 46:10. The plan of God is also unchangeable, because He is faithful and true, Job 28:13, 14; Isa. 46:10; Luke 22:22.

Louis Berkhof, Summary of Christian Doctrine, VIII. 1. a.