Do evil spirits have power over souls?

Indeed, from my own experience, and from what I have seen in others, I can testify to the awful truth that an evil spirit has power over human souls. 

How often someone has formed the best of resolutions, he has turned from sin and is anxious to seek the way of life, but the tempter enters his heart and he falls deeper than before.

And then to say there is no devil!

Devil? 

Yes, it is no use mincing an awful fact—

It is he who drags man to hell. 

There is a devil, and the number of demons is legion.

But—say you—how is it that God—the strong, righteous, pitiful God—allows the evil one such terrible power over human souls? 

Can He be the all-loving, all-merciful Father if He does not snatch them from the destroyer even at the moment of their weakness?

Do you doubt God, my friend? 

Was it not He who sent his good angels to watch the door of your heart―who put all that trouble and anguish into you―who made you feel and tremble at the burden of your sin? 

Ay, it is His Spirit who is at work in you when you feel you have done wrong―when you long to rise to a better life. 

It is He who shows you that you can rise if only you will!

But your will is at fault—your sincerity.

That is it! 

What God does for you even at such decisive moments is immeasurably more than what the devil can do. 

But to God, you listen not―great as His love is―you care not for the riches of grace with which He tries to save you―whereas the devil need but pipe and you straightway are ready to do his bidding. 

Is it to be marvelled at that there is nothing left for you but to go to hell?

Letters from Hell