"Have they not seen that We have made a secure sanctuary," meaning: Yes, they have indeed seen that. "While people are being snatched away from all around them," meaning: the people of the Sanctuary. He is saying: They are secure, while the Arabs around them are killing one another. "Do they then believe in falsehood?" meaning: Do they believe in Iblis? That is: in what he whispered to them of idol worship, which is his worship. "And they deny the favor of Allah," meaning: what the Prophet (peace be upon him) brought of guidance. This is in the form of a question; meaning: they have indeed done so.