anon, those who are called by His Name are His forever. There are only 2 type of ppl in this world, sheep or goats. A person is either His or they are not. He calls those whom are His and they come. Those who are not His do not hear Him.
"But because you are not My sheep, you refuse to believe. My sheep listen to My voice; I know them, and they follow Me. I give them eternal life, and they will never perish. No one can snatch them out of My hand.…"
They dont switch back and forth. If they do, they are false.
"They went out from us, but they were not really of us; for if they had been of us, they would have remained with us; but they went out, so that it would be shown that they all are not of us."