Frank Turek is a popular teacher nowadays. He seems to be preaching the true Gospel at first but then he reveals his true theology about assurance of salvation because he believes assurance does not come from Jesus Christ and his finished work, but from your own personal conviction of sin. None of us have perfect conviction we still "live in sin" every day without knowing or remembering all of our sins. It's a damnable and subtle heresy to be watchful for. God bless.