Regeneration is something that can never be lost

Regeneration is something that can never be lost. If you are regenerate, you will remain regenerate. It seems to me that this is absolutely inevitable because regeneration is the work of God. Yet there are those who seem to think that people can be born again as the result of believing the truth and then, if they backslide or fall into sin or deny the truth, they lose their regeneration. But if they come back again and believe again, then they are regenerate again — as if one can be born again and die and be born again and die an endless number of times! How important doctrine is! How important it is that we should be clear as to what the Scripture teaches about these things! It tells us that regeneration is the work of God Himself in the depths of the soul and that He does it in such a way that it is permanent. ‘No man is able to pluck them out of my Father’s hand’ ( John 10:29 ).

- D Martyn Lloyd-Jones
Effectual Calling and Regeneration