There is a popular church that sends young missionaries door to door. They will tell you that there was a complete apostasy of the Christian church and their founding prophet was given the restored gospel, making theirs the only true church on the face of the earth.
If you read these verses carefully, you will see where the lie is. The Bible says "many" will follow these false teachers. "Many" does not equal a complete apostasy. If there was a complete apostasy the verse would have to say all would follow these false teachers. Don't be fooled.
How do you know false teachers and prophets? Know your Bible! Study the Word. Get so familiar with the Word that you will spot false teaching the minute it comes along.
Peter keeps emphasizing the need for knowledge of Jesus Christ and His Word. It's so important! Learn the Word! It's your defense against doctrinal error.