So why, if God is all powerful...?

Can one not exist without the other?

The entrance of Jesus Christ into the history of the world reaches its culmination in the Paschal Mystery, where nature itself takes part in the drama of the rejection of the Son of God and in the victory of his Resurrection (cf. Mt 27:45,51, 28:2). Crossing through death and grafting onto it the new splendour of the Resurrection, Jesus inaugurates a new world in which everything is subjected to him (cf. 1 Cor 15:20-28) and he creates anew those relationships of order and harmony that sin had destroyed. Knowledge of the imbalances existing between man and nature should be accompanied by an awareness that in Jesus the reconciliation of man and the world with God — such that every human being, aware of divine love, can find anew the peace that was lost — has been brought about. “Therefore, if any one is in Christ, he is a new creation; the old has passed away, behold, the new has come” (2 Cor 5:17). Nature, which was created in the Word is, by the same Word made flesh, reconciled to God and given new peace (cf. Col 1:15-20).

It’s all a part of the free will He gave us. The devil is an necessary evil for God’s fulfillment of man and His plan.

So is He all powerful or not?