What does Matthew 24:25 mean?

Jesus wants His disciples to remember that He warned them about these unique things which would happen. This forewarning serves several different purposes. First it makes hardships easier to endure. Simply knowing that there is a plan, an end, and a victory at the end of suffering makes it much easier to "hold fast" under stress (John 16:1–4; Hebrews 10:23).

Another advantage is that as prophesied events come to pass, Jesus' followers will be confirmed in their faith (Hebrews 12:1). There is great encouragement in being able to read the words of Christ, and to say, "He told us this would happen, and now it has."

Third, Jesus' words will help to keep the disciples from falling for ungodly lies and manipulations. Those who listen to Christ's predictions, and warnings (Matthew 24:4–5, 11, 24) won't be drawn in by displays of power from false saviors or other impostors. Instead, they will remember Jesus' words. He is equipping them to defeat the lies of tomorrow with truth in the present.

Jesus echoes Isaiah 48:5, speaking about one purpose of prophesy: "I declared them to you from of old, before they came to pass I announced them to you, lest you should say, 'My idol did them, my carved image and my metal image commanded them.'"