The mass of modern and postmodern evangelicals simply ignore this command. I'm tempted to say they rebel against it. Many are simply too arrogant to think they need an admonition like this. They carelessly think they are skilled enough and knowledgeable enough to recognize any and every error at its very first appearance, so they have let down their guard.
Mostly, though, evangelicals simply have no stomach for the duty—and they won't tolerate it if anyone else tries to interrupt the evangelical frat party with shrill alarms—even while the frat house is engulfed in flames.
We don't mind reading about Spurgeon's courage and foresight in the Down-Grade Controversy; we just don't want anyone today to exercise that kind of discernment. In fact, listen to what Spurgeon said about that very same phenomenon in his era:
It is very pretty, is it not, to read of Luther and his brave deeds? Of course, everybody admires Luther! Yes, yes; but you do not want any one else to do the same to-day. When you go to the [zoo] you all admire the bear; but how would you like a bear at home, or a bear wandering loose about the street? You tell me that it would be unbearable, and no doubt you are right.
So, we admire a man who was firm in the faith, say four hundred years ago; the past ages are a sort of bear-pit or iron cage for him; but such a man to-day is a nuisance, and must be put down. Call him a narrow-minded bigot, or give him a worse name if you can think of one. Yet imagine [if] in those ages past, Luther, Zwingle, Calvin, and their compeers had said, "The world is out of order; but if we try to set it right we shall only make a great row, and get ourselves into disgrace. Let us go to our chambers, put on our night-caps, and sleep over the bad times, and perhaps when we wake up things will have grown better." Such conduct on their part would have entailed upon us a heritage of error. Age after age would have gone down into the infernal deeps, and the pestiferous bogs of error would have swallowed all. These men loved the faith and the name of Jesus too well to see them trampled on.The need for vigilance today is greater, not less, than it has been in times past.
When before our very eyes we can see "evil people and impostors [going] from bad to worse, deceiving and being deceived"—it is more important than ever to stay alert and on guard against false teaching and against personal temptations. And it's more important than ever to make ourselves ready for the return of the Savior.
That's what Paul was telling the Corinthians: "Be watchful"—first of all over yourselves—your hearts, your passions, your words, and your whole way of life. Be watchful over one another, lest you fall into sin and temptation. Be on guard against Satan, "so that we would not be outwitted by [him]; for we are not ignorant of his designs." Likewise, be on guard against false teachers, who lie in wait to deceive and who have already begun to sow their deception in your midst. Be on guard against the world, with all its snares and seductions. Also, watch unto prayer, and prepare yourselves for the Lord's return.
All of that is packed into this one-word admonition: "Watch."