This verse is unsettling to me and has been since I heard it. First it was just a matter of assurance of salvation and the fear of one day hearing those words. Being turned away from heaven with those words would be awful.
Taking it deeper though it makes me question the immediacy and guarantee of salvation. Can salvation truly be traced back to the instant that a person prays a prayer and ‘asks Christ into their lives’? Even if they mean it and have faith and all that. It specifies the condition of Christ knowing us. In that direction. How could Christ know us the second we pray that prayer? Because technically Christ is God, therefore God/Christ claims to know us intimately (knowing the number of hairs on our heads) even when we aren’t ‘saved’. So if he knows everything about us before we pray the prayer and we aren’t saved then knowing in this sense must refer to something more. This knowing would be active, choosing to share our happiness, trials and learning. Choosing time to get to know Christ. This can’t have been done that quickly can it? So when does Christ ‘know’ us?