As God decreed before the foundations of the world in eternity past to glorify Himself - not because there was a need of God but because the glory of God is instrinsic to who He is and His nature so that what He does and how He reveals Himself cannot be seperated from His divine being. That God chose within Himself to Glorify Himself (Father, Son, and Holy Spirit and to make known His divine attributes) can only be but apart from any considerations of the creature or any other created thing. What God does is completely free and sovereign and is by His own free uncoercive choice and pleasure. What does this mean other than what happens in this world is already predetermined by the sovereign will of the triune God. That Christ was chosen to be the mediator of a particular persons and that His work was intended to bring about the sole redemption of those persons is based upon the choice of the whole person of who the mediator would be. That the relationship between the Head (Christ) and the Body (the Church was so natural that nothing was added to it or had to be touched upon later. That the Holy Spirit would honor the head by applying the redeming work of Christ to the Body of Christ.
Now If I might further say that God had also reprobated certians ones for the very purpose of bringout His divine pleasure in the making known who are the elect, and who is the Christ and His work.
Read: Abraham Kuyper, Herman Hoeksema, and Geerhardus Vos for more information and clarification
