"We cannot always be sure exactly when regeneration has taken place. It is clearly not a gradual thing, however. It is something sudden and instantaneous. The very way the Bible describes new birth suggests this. ... Some resist the idea. Opposition often grows out of misunderstanding. To understand regeneration correctly we must keep it distinct in our minds from what leads up to it and what follows. However near to it or far from it a man may be, he is either born again or not born again. The idea of a gradual
or progressive regeneration would mean that one could be half-regenerate, half-unregenerate; in a twilight zone, partly in the kingdom, partly outside it; not dead and not alive either; neither new creation nor old.
Such an idea runs contrary to the Bible’s teaching."
From my book What the Bible teaches about being born again, pp 31, 32