A wicked and adulterous generation looks for a miraculous sign, but none will be given it except the sign of Jonah. Jesus then left them and went away. Jesus essentially scolded them for their inability to understand truly spiritual things. Like them, we seem to have lost our ability to discern theological truth from error. Distinguishing between truth and error is essential in the Christian life - both for individuals and the church at large.
Christians are to examine everything very carefully.
By doing this, Scripture tells us that we will be able to distinguish truth from error. Furthermore, Scripture admonishes us to cling to truth and to shun error. This is why it is so vital for Christians to become more discerning. Of course, I am not the first to sound this alarm. Faithful men and women have been making this appeal for 2,000 years.