This question has been debated for centuries…so I suppose I may be permitted a brief opinion.
The commonly held view is that we lose salvation by apostasy, and certainly that is supported in Scripture – a deliberate turning away from Christ is a fatal act.
However…I would posit that while we may not deliberately renounce Christ, our daily actions often amount to a total renunciation of all that He is.
So many of us lie. We exaggerate our successes or our hurts to gain accolades or attention.
We cheat. We may sell some items for more than their purchase price on eBay, but as long as the sums are modest, the IRS does not typically question our figures…so we may invent a loss, or a more modest profit that we actually derived.
We lust. The television programmes we watch cater to the development of lustful thoughts, but we do not turn away.
Would we do this if Christ were watching?
No, but we assume He isn’t watching. It’s a tacit assumption that He isn’t there, at least when we’f rather He not be.
I think we are denying Him, far more seriously than we know.
And we risk much.