What Jesus was trying to say here is that it does oneself no good in the long run to believe in the Power of Christ if one does not bother knowing Christ. From the beginning, it has always been about relationship. God is looking for a family. He gives freely to those who ask, but in the end, He is still looking for a family. Those in Matthew 7 asked for and were given the power of Christ. They even recognized Jesus as Lord, but they never put forth the effort to get to know Him.
I already pointed out that the Matthew 7 passage was about false prophets, and that Matthew 24 itself acknowledges the power of false prophets, and their deceitfulness...wolves in sheep’s clothing.
So, all I have to do is use the bible to explain itself in this question you’ve posed.
The bible says that we wrestle not with flesh and blood, but with dark powers and principalities.
So, if Satan can appear as an angel of light, and his minions can be deceitful and powerful, then we would simply be finding in the bible examples of those who’ve pretended to be on the Lord’s side, but have actually been powered otherwise.
Acts 4: 4 The two of them, sent on their way by the Holy Spirit, went down to Seleucia and sailed from there to Cyprus. 5 When they arrived at Salamis, they proclaimed the word of God in the Jewish synagogues. John was with them as their helper. 6 They traveled through the whole island until they came to Paphos. There they met a Jewish sorcerer and false prophet named Bar-Jesus, 7 who was an attendant of the proconsul, Sergius Paulus. The proconsul, an intelligent man, sent for Barnabas and Saul because he wanted to hear the word of God. 8 But Elymas the sorcerer (for that is what his name means) opposed them and tried to turn the proconsul from the faith. 9 Then Saul, who was also called Paul, filled with the Holy Spirit, looked straight at Elymas and said, 10 “You are a child of the devil and an enemy of everything that is right! You are full of all kinds of deceit and trickery. Will you never stop perverting the right ways of the Lord? 11 Now the hand of the Lord is against you. You are going to be blind, and for a time you will be unable to see the light of the sun.” Immediately mist and darkness came over him, and he groped about, seeking someone to lead him by the hand. 12 When the proconsul saw what had happened, he believed, for he was amazed at the teaching about the Lord.