A Christian is a follower of Christ, someone who is saved.
He does not have on again/off again salvation depending on his works.
That teaching makes salvation a works based merit system.
A Christian's salvation is secure because the Christian is in Christ, a new creature in Christ, born from above, transferred into the kingdom of the Son God loves, seated with Christ in the heavenly places.
Any sin that he has not repented of is covered anyway and will not cost him his salvation.
Any teaching that a Christian can go to hell for sin committed is wrong because Christian is saved.
It is hell they are saved from.
If they go to hell because of sin committed, then they are not saved from hell, therefore not Christians.
So this teaching that a Christian can go to hell is right from the pit of hell itself.