Jesus says:
My sheep hear My voice, and I know them, and they follow Me:
And I give unto them eternal life; and they shall never perish, neither shall any pluck them out of My hand.
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The shepherd speaks. The sheep recognize his voice. Even a new sheep comes to know his voice.
And they follow Him.
John 10:4-5 And when He putteth forth His own sheep, He goeth before them, and the sheep follow Him: for they know His voice.
And a stranger will they not follow, but will flee from him: for they know not the voice of strangers.
And a stranger will they not follow, but will flee from him: for they know not the voice of strangers.
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