Before the foundation of the world, God the Father, Jesus Christ the Son, and the holy spirit designed a plan that would bring glory to the God the Father through creation, He did that so that He would have a people to be called His own and designed it that way and for Him to be glorified in the process.
Jesus' death on the cross and redeeming us wasn't an afterthought to Adam sinning in the garden of Eden, it was God's plan all along that things would happen that way, and He did things as to maximize the glory He receives from His creation, all the evil in the world isn't meaningless, it all has a purpose and you can believe me or not, but even actions intended as evil by men are intended for good by God, as Paul said was the case in Jesus going to calvary, it was the result of actions by 4 groups of people, yet God had designed that to be the means by which Christ would die and redeem us, yet He's still just and punishes evildoers for their actions, even if God intended them for good.
In the reformed faith, salvation is a work of the triune God: God the Father elected us to be saved, Jesus the Son died in our place and received the just compensation for our sins and the holy spirit works in those who God the Father elected and those people then believe in Christ and his work at cavalry, no one can believe if the holy spirit doesn't convict them first.