The heart is deceitful above all things, and desperately wicked: who can know it? Jeremiah 17:9 KJV https://bible.com/bible/1/jer.17.9.KJV
The heart of mankind is where your true self lives. If you have given your heart to Jesus, then you are a new creation. If you haven’t your heart can deceive you into thinking that you are a Christian when you are not.
There have been some preachers who have been to school and seminary and yet they found that one day they were not saved. You can go through the motions and still not be saved! God knows your heart, but your own heart can trick you into thinking that you are saved even though it’s a lie.
Seek your Savior, Jesus, while there’s time to do so. If you’re still breathing you can still come to Christ. Amen