Why not remains for a while or abides for a while? Why must you believe he was saved for a while?
I'll tell you God doesn't save for a while.
I think it would be more accurate to say if a man is not rooted in love, he remains in Christ only for a while or he abides in Christ only for a while, and then he is broken off and burned.
If he believes for 5 years then because of persecution, he turns away from Christ, he is no longed saved.
JLB