The Bible warns about deception in the last days because it will become more rampant and widespread. In 2 Thessalonians 2:9-12, it says: "The coming of the lawless one will be in accordance with the work of Satan displayed in all kinds of counterfeit miracles, signs and wonders, and in every sort of evil that deceives those who are perishing. They perish because they refused to love the truth and so be saved. For this reason God sends them a powerful delusion so that they will believe the lie and so that all will be condemned who have not believed the truth but have delighted in wickedness." So, we can see that there is a specific purpose for why God warns us about deception in the last days. He does it so that we will be able to recognize deception when we see it and not be deceived by it.