Their acts are meant to put fear into the hearts of Christ followers. But here is what Isis does not know.
One: The evil one thought he had won the battle against God when Christ was crucified. What he did not count on was the resurrection of Christ. At that moment every principality and power of this world was defeated and all they can do until Christ returns is fight a losing battle. Neither Isis or any other group will ever break the cross.
Two: When the church is under persecution it expands rather than contracts. Mao thought he could eradicate the church. What resulted is the largest church in the world. In Roman times, the rulers thought they could eradicate the church but three hundred years after Christ, Christianity became the official faith of the Roman empire. As Tertullian wrote, "The blood of the martrys is the seed of the church." Every time Isis tries to eradicate Christianity more people come to Christ. It is a losing battle. Again to quote Tertullian, "The more you mow us down, the more numerous we grow; the blood of Christians is seed."
Three: While evil can prevail for a time it ultimately loses and is judged by the God of the Universe. History is His story and His will is the only one that will ultimately prevail. He is the beginning and the end! The alpha and omega. There will be a new heaven and earth and Christ will reign over all.
As Christ followers we need to keep these three truths in mind as we watch the news and rather than live in fear we ought to live with the conviction that Christ is growing His church and that He will ultimately prevail.