The devil can do nothing in the life of the Christian without God's permission.
This may come as a surprise, but the devil does have some access to Heaven. Periodically the devil is called into the presence of God. We have a behind-the-scenes look at this in the book of Job:
Now there was a day when the sons of God came to present themselves before the LORD, and Satan also came among them. And the LORD said to Satan, "From where do you come?"So Satan answered the LORD and said, "From going to and fro on the earth, and from walking back and forth on it." (Job 1:6–7)
What a perfect description of Satan—just roaming about like a lion, checking everything out, looking for prey.
Then God said, "Have you considered My servant Job, that there is none like him on the earth, a blameless and upright man, one who fears God and shuns evil?" (verse 8).
Loosely paraphrased, the devil said, "Give me a break! Does Job fear You for nothing? He fears you because You have put a hedge of protection around him."
The devil wanted to attack Job, but he recognized there was protection around God's servant.
And there is protection around us as well. When the devil comes our way, he has to first get permission from God. He cannot just run through our lives willy-nilly. And know this: Whatever God allows in your life, He allows for a purpose.
Sometimes we wonder why the Lord allows tragedies in our lives. While we can't answer that, what we do know is this: God will never give us more than we can handle. And when we are tempted, there is always a way out.